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  • Direct measurement of internal magnetic fields in natural sands using scanning SQUID microscopy JOURNAL OF MAGNETIC RESONANCE Walbrecker, J. O., Kalisky, B., Grombacher, D., Kirtley, J., Moler, K. A., Knight, R. 2014; 242: 10-17

    Abstract

    NMR experiments are ideally carried out in well-controlled magnetic fields. When samples of natural porous materials are studied, the situation can be complicated if the sample itself contains magnetic components, giving rise to internal magnetic fields in the pore space that modulate the externally applied fields. If not properly accounted for, the internal fields can lead to misinterpretation of relaxation, diffusion, or imaging data. To predict the potential effect of internal fields, and develop effective mitigation strategies, it is important to develop a quantitative understanding of the magnitude and distribution of internal fields occurring in natural porous media. To develop such understanding, we employ scanning SQUID microscopy, a technique that can detect magnetic field variations very accurately at high spatial resolution (∼3μm). We prepared samples from natural unconsolidated aquifer material, and scanned areas of about 200×200μm in a very low background magnetic field of ∼2μT. We found large amplitude variations with a magnitude of about 2mT, across a relatively long spatial scale of about 200μm, that are associated with a large magnetic grain (>50μm radius) with a strong magnetic remanence. We also detected substantial variations exceeding 60μT on small spatial scales of about ∼10μm. We attribute these small-scale variations to very fine-grained magnetic material. Because we made our measurements at very low background field, the observed variations are not induced by the background field but due to magnetic remanence. Consequently, the observed internal fields will affect even low-field NMR experiments.

    View details for DOI 10.1016/j.jmr.2014.01.012

    View details for Web of Science ID 000336472600003

    View details for PubMedID 24589519

  • Locally enhanced conductivity due to the tetragonal domain structure in LaAlO3/SrTiO3 heterointerfaces. Nature materials Kalisky, B., Spanton, E. M., Noad, H., Kirtley, J. R., Nowack, K. C., Bell, C., Sato, H. K., Hosoda, M., Xie, Y., Hikita, Y., Woltmann, C., Pfanzelt, G., Jany, R., Richter, C., Hwang, H. Y., Mannhart, J., Moler, K. A. 2013; 12 (12): 1091-1095

    Abstract

    The ability to control materials properties through interface engineering is demonstrated by the appearance of conductivity at the interface of certain insulators, most famously the {001} interface of the band insulators LaAlO3 and TiO2-terminated SrTiO3 (STO; refs , ). Transport and other measurements in this system show a plethora of diverse physical phenomena. To better understand the interface conductivity, we used scanning superconducting quantum interference device microscopy to image the magnetic field locally generated by current in an interface. At low temperature, we found that the current flowed in conductive narrow paths oriented along the crystallographic axes, embedded in a less conductive background. The configuration of these paths changed on thermal cycling above the STO cubic-to-tetragonal structural transition temperature, implying that the local conductivity is strongly modified by the STO tetragonal domain structure. The interplay between substrate domains and the interface provides an additional mechanism for understanding and controlling the behaviour of heterostructures.

    View details for DOI 10.1038/nmat3753

    View details for PubMedID 24013791

  • Imaging currents in HgTe quantum wells in the quantum spin Hall regime. Nature materials Nowack, K. C., Spanton, E. M., Baenninger, M., König, M., Kirtley, J. R., Kalisky, B., Ames, C., Leubner, P., Brüne, C., Buhmann, H., Molenkamp, L. W., Goldhaber-Gordon, D., Moler, K. A. 2013; 12 (9): 787-791

    Abstract

    The quantum spin Hall (QSH) state is a state of matter characterized by a non-trivial topology of its band structure, and associated conducting edge channels. The QSH state was predicted and experimentally demonstrated to be realized in HgTe quantum wells. The existence of the edge channels has been inferred from local and non-local transport measurements in sufficiently small devices. Here we directly confirm the existence of the edge channels by imaging the magnetic fields produced by current flowing in large Hall bars made from HgTe quantum wells. These images distinguish between current that passes through each edge and the bulk. On tuning the bulk conductivity by gating or raising the temperature, we observe a regime in which the edge channels clearly coexist with the conducting bulk, providing input to the question of how ballistic transport may be limited in the edge channels. Our results represent a versatile method for characterization of new QSH materials systems.

    View details for DOI 10.1038/nmat3682

    View details for PubMedID 23770727

  • Imaging currents in HgTe quantum wells in the quantum spin Hall regime. Nature materials Nowack, K. C., Spanton, E. M., Baenninger, M., König, M., Kirtley, J. R., Kalisky, B., Ames, C., Leubner, P., Brüne, C., Buhmann, H., Molenkamp, L. W., Goldhaber-Gordon, D., Moler, K. A. 2013; 12 (9): 787-791

    Abstract

    The quantum spin Hall (QSH) state is a state of matter characterized by a non-trivial topology of its band structure, and associated conducting edge channels. The QSH state was predicted and experimentally demonstrated to be realized in HgTe quantum wells. The existence of the edge channels has been inferred from local and non-local transport measurements in sufficiently small devices. Here we directly confirm the existence of the edge channels by imaging the magnetic fields produced by current flowing in large Hall bars made from HgTe quantum wells. These images distinguish between current that passes through each edge and the bulk. On tuning the bulk conductivity by gating or raising the temperature, we observe a regime in which the edge channels clearly coexist with the conducting bulk, providing input to the question of how ballistic transport may be limited in the edge channels. Our results represent a versatile method for characterization of new QSH materials systems.

    View details for DOI 10.1038/nmat3682

    View details for PubMedID 23770727

  • Direct measurement of current-phase relations in superconductor/topological insulator/superconductor junctions. Nano letters Sochnikov, I., Bestwick, A. J., Williams, J. R., Lippman, T. M., Fisher, I. R., Goldhaber-Gordon, D., Kirtley, J. R., Moler, K. A. 2013; 13 (7): 3086-3092

    Abstract

    Proximity to a superconductor is predicted to induce exotic quantum phases in topological insulators. Here, scanning superconducting quantum interference device (SQUID) microscopy reveals that aluminum superconducting rings with topologically insulating Bi2Se3 junctions exhibit a conventional, nearly sinusoidal 2π-periodic current-phase relations. Pearl vortices occur in longer junctions, indicating suppressed superconductivity in aluminum, probably due to a proximity effect. Our observations establish scanning SQUID as a general tool for characterizing proximity effects and for measuring current-phase relations in new materials systems.

    View details for DOI 10.1021/nl400997k

    View details for PubMedID 23795666

  • Direct Measurement of Current-Phase Relations in Superconductor/Topological Insulator/Superconductor Junctions NANO LETTERS Sochnikov, I., Bestwick, A. J., Williams, J. R., Lippman, T. M., Fisher, I. R., Godhaber-Gordon, D., Kirtley, J. R., Moler, K. A. 2013; 13 (7): 3086-3092

    View details for DOI 10.1021/nl400997k

    View details for Web of Science ID 000321884300014

  • Advanced sensors for scanning SQUID microscopy 2013 IEEE 14TH INTERNATIONAL SUPERCONDUCTIVE ELECTRONICS CONFERENCE (ISEC) Kirtley, J. R., Gibson, G. W., Fung, Y. K., KLOPFER, B., Nowack, K., Kratz, P. A., Mol, J., Arpes, J., Forooghi, F., Huber, M. E., Bluhm, H., Moler, K. A. 2013
  • Agreement between local and global measurements of the London penetration depth PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS Lippman, T. M., Kalisky, B., Kim, H., Tanatar, M. A., Bud'ko, S. L., Canfield, P. C., Prozorov, R., Moler, K. A. 2012; 483: 91-93
  • Gate-tuned superfluid density at the superconducting LaAlO3/SrTiO3 interface PHYSICAL REVIEW B Bert, J. A., Nowack, K. C., Kalisky, B., Noad, H., Kirtley, J. R., Bell, C., Sato, H. K., Hosoda, M., Hikita, Y., Hwang, H. Y., Moler, K. A. 2012; 86 (6)
  • Scanning Probe Manipulation of Magnetism at the LaAlO3/SrTiO3 Heterointerface NANO LETTERS Kalisky, B., Bert, J. A., Bell, C., Xie, Y., Sato, H. K., Hosoda, M., Hikita, Y., Hwang, H. Y., Moler, K. A. 2012; 12 (8): 4055-4059

    Abstract

    Manipulation of magnetism is a longstanding goal of research in exotic materials. In this work, we demonstrate that the small ferromagnetic patches in LaAlO(3)/SrTiO(3) heterostructures can be dramatically changed by in situ contact of a scanning probe. Our results provide a platform for manipulation of small magnets through either a strong magneto-elastic coupling or sensitivity to surface modification. The ability to locally control magnetism is particularly interesting due to the presence of superconductivity with strong spin-orbit coupling in LaAlO(3)/SrTiO(3).

    View details for DOI 10.1021/nl301451e

    View details for Web of Science ID 000307211000030

    View details for PubMedID 22769056

  • Scanning SQUID susceptometry of a paramagnetic superconductor PHYSICAL REVIEW B Kirtley, J. R., Kalisky, B., Bert, J. A., Bell, C., Kim, M., Hikita, Y., Hwang, H. Y., Ngai, J. H., Segal, Y., Walker, F. J., Ahn, C. H., Moler, K. A. 2012; 85 (22)
  • Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures NATURE COMMUNICATIONS Kalisky, B., Bert, J. A., Klopfer, B. B., Bell, C., Sato, H. K., Hosoda, M., Hikita, Y., Hwang, H. Y., Moler, K. A. 2012; 3

    Abstract

    In LaAlO(3)/SrTiO(3) heterointerfaces, charge carriers migrate from the LaAlO(3) to the interface in an electronic reconstruction. Magnetism has been observed in LaAlO(3)/SrTiO(3), but its relationship to the interface conductivity is unknown. Here we show that reconstruction is necessary, but not sufficient, for the formation of magnetism. Using scanning superconducting quantum interference device microscopy we find that magnetism appears only above a critical LaAlO(3) thickness, similar to the conductivity. We observe no change in ferromagnetism with gate voltage, and detect ferromagnetism in a non-conducting p-type sample. These observations indicate that the carriers at the interface do not need to be itinerant to generate magnetism. The ferromagnetism appears in isolated patches whose density varies greatly between samples. This inhomogeneity strongly suggests that disorder or local strain generates magnetism in a population of the interface carriers.

    View details for DOI 10.1038/ncomms1931

    View details for Web of Science ID 000306099900049

    View details for PubMedID 22735450

  • Calculation of the effect of random superfluid density on the temperature dependence of the penetration depth PHYSICAL REVIEW B Lippman, T. M., Moler, K. A. 2012; 85 (10)
  • Fluxoid fluctuations in mesoscopic superconducting rings PHYSICAL REVIEW B Bert, J. A., Koshnick, N. C., Bluhm, H., Moler, K. A. 2011; 84 (13)
  • Pattern-Free Growth of Carbon Nanotube Tips for Scanning Probe Microscopy NANOSCIENCE AND NANOTECHNOLOGY LETTERS Yenilmez, E., Zhang, H., Zhang, L., Deng, Z., Moler, K. A. 2011; 3 (5): 669-673
  • Direct imaging of the coexistence of ferromagnetism and superconductivity at the LaAlO3/SrTiO3 interface NATURE PHYSICS Bert, J. A., Kalisky, B., Bell, C., Kim, M., Hikita, Y., Hwang, H. Y., Moler, K. A. 2011; 7 (10): 767-771

    View details for DOI 10.1038/nphys2079

    View details for Web of Science ID 000295584200013

  • Behavior of vortices near twin boundaries in underdoped Ba(Fe1-xCox)(2)As-2 PHYSICAL REVIEW B Kalisky, B., Kirtley, J. R., Analytis, J. G., Chu, J., Fisher, I. R., Moler, K. A. 2011; 83 (6)
  • Local Measurement of the Superfluid Density in the Pnictide Superconductor Ba(Fe1-xCox)(2)As-2 across the Superconducting Dome PHYSICAL REVIEW LETTERS Luan, L., Lippman, T. M., Hicks, C. W., Bert, J. A., Auslaender, O. M., Chu, J., Analytis, J. G., Fisher, I. R., Moler, K. A. 2011; 106 (6)

    Abstract

    We measure the penetration depth ?ab(T) in Ba(Fe(1-x)Co(x))(2)As(2) using local techniques that do not average over the sample. The superfluid density ?s(T) ? 1/?ab(T)2 has three main features. First, ?s (T = 0) falls sharply on the underdoped side of the dome. Second, ?ab(T) is flat at low T at optimal doping, indicating fully gapped superconductivity, but varies more strongly in underdoped and overdoped samples, consistent with either a power law or a small second gap. Third, ?s (T) varies steeply near Tc for optimal and underdoping. These observations are consistent with an interplay between magnetic and superconducting phases.

    View details for DOI 10.1103/PhysRevLett.106.067001

    View details for Web of Science ID 000287135400006

    View details for PubMedID 21405485

  • HIGH-TEMPERATURE SUPERCONDUCTIVITY How the cuprates hid their stripes NATURE Moler, K. A. 2010; 468 (7324): 643-644

    View details for Web of Science ID 000284836700028

    View details for PubMedID 21124446

  • Limits on superconductivity-related magnetization in Sr2RuO4 and PrOs4Sb12 from scanning SQUID microscopy PHYSICAL REVIEW B Hicks, C. W., Kirtley, J. R., Lippman, T. M., Koshnick, N. C., Huber, M. E., Maeno, Y., Yuhasz, W. M., Maple, M. B., Moler, K. A. 2010; 81 (21)
  • Meissner response of a bulk superconductor with an embedded sheet of reduced penetration depth PHYSICAL REVIEW B Kirtley, J. R., Kalisky, B., Luan, L., Moler, K. A. 2010; 81 (18)
  • Stripes of increased diamagnetic susceptibility in underdoped superconducting Ba(Fe(1-x)Cox)(2)As-2 single crystals: Evidence for an enhanced superfluid density at twin boundaries PHYSICAL REVIEW B Kalisky, B., Kirtley, J. R., Analytis, J. G., Chu, J., Vailionis, A., Fisher, I. R., Moler, K. A. 2010; 81 (18)
  • Local measurement of the penetration depth in the pnictide superconductor Ba(Fe0.95Co0.05)(2)As-2 PHYSICAL REVIEW B Luan, L., Auslaender, O. M., Lippman, T. M., Hicks, C. W., Kalisky, B., Chu, J., Analytis, J. G., Fisher, I. R., Kirtley, J. R., Moler, K. A. 2010; 81 (10)
  • Sequential vortex hopping in an array of artificial pinning centers PHYSICAL REVIEW B Keay, J. C., Larson, P. R., Hobbs, K. L., Johnson, M. B., Kirtley, J. R., Auslaender, O. M., Moler, K. A. 2009; 80 (16)
  • Evidence for a Nodal Energy Gap in the Iron-Pnictide Superconductor LaFePO from Penetration Depth Measurements by Scanning SQUID Susceptometry PHYSICAL REVIEW LETTERS Hicks, C. W., Lippman, T. M., Huber, M. E., Analytis, J. G., Chu, J., Erickson, A. S., Fisher, I. R., Moler, K. A. 2009; 103 (12)

    Abstract

    We measure changes in the penetration depth lambda of the T_{c} approximately 6 K superconductor LaFePO. In the process, scanning SQUID susceptometry is demonstrated as a technique for accurately measuring local temperature-dependent changes in lambda, ideal for studying early or difficult-to-grow materials. lambda is found to vary linearly with temperatures from 0.36 to approximately 2 K, with a slope of 143 +/- 15 A/K, suggesting line nodes in the superconducting order parameter. The linear dependence up to approximately T_{c}/3, similar to the cuprate superconductors, indicates well-developed nodes.

    View details for DOI 10.1103/PhysRevLett.103.127003

    View details for Web of Science ID 000270139000041

    View details for PubMedID 19792454

  • Spinlike Susceptibility of Metallic and Insulating Thin Films at Low Temperature PHYSICAL REVIEW LETTERS Bluhm, H., Bert, J. A., Koshnick, N. C., Huber, M. E., Moler, K. A. 2009; 103 (2)

    Abstract

    Susceptibility measurements of patterned thin films at sub-K temperatures were carried out using a scanning SQUID microscope that can resolve signals corresponding to a few hundred Bohr magnetons. Several metallic and insulating thin films, even oxide-free Au films, show a paramagnetic response with a temperature dependence that indicates unpaired spins as the origin. The observed response exhibits a measurable out-of-phase component, which implies that these spins will create 1/f-like magnetic noise. The measured spin density is consistent with recent explanations of low frequency flux noise in SQUIDs and superconducting qubits in terms of spin fluctuations, and suggests that such unexpected spins may be even more ubiquitous than already indicated by earlier measurements. Our measurements set several constraints on the nature of these spins.

    View details for DOI 10.1103/PhysRevLett.103.026805

    View details for Web of Science ID 000267887800048

    View details for PubMedID 19659233

  • Magnetic force microscopy study of interlayer kinks in individual vortices in the underdoped cuprate superconductor YBa2Cu3O6+x PHYSICAL REVIEW B Luan, L., Auslaender, O. M., Bonn, D. A., Liang, R., Hardy, W. N., Moler, K. A. 2009; 79 (21)
  • Dynamics of single vortices in grain boundaries: I-V characteristics on the femtovolt scale APPLIED PHYSICS LETTERS Kalisky, B., Kirtley, J. R., Nowadnick, E. A., Dinner, R. B., Zeldov, E., Ariando, Wenderich, S., Hilgenkamp, H., Feldmann, D. M., Moler, K. A. 2009; 94 (20)

    View details for DOI 10.1063/1.3137164

    View details for Web of Science ID 000266342800041

  • Persistent Currents in Normal Metal Rings PHYSICAL REVIEW LETTERS Bluhm, H., Koshnick, N. C., Bert, J. A., Huber, M. E., Moler, K. A. 2009; 102 (13)

    Abstract

    The authors have measured the magnetic response of 33 individual cold mesoscopic gold rings, one ring at a time. The response of some sufficiently small rings has a component that is periodic in the flux through the ring and is attributed to a persistent current. Its period is close to h/e, and its sign and amplitude vary between rings. The amplitude distribution agrees well with predictions for the typical h/e current in diffusive rings. The temperature dependence of the amplitude, measured for four rings, is also consistent with theory. These results disagree with previous measurements of three individual metal rings that showed a much larger periodic response than expected. The use of a scanning SQUID microscope enabled in situ measurements of the sensor background. A paramagnetic linear susceptibility and a poorly understood anomaly around a zero field are attributed to defect spins.

    View details for DOI 10.1103/PhysRevLett.102.136802

    View details for Web of Science ID 000264888600051

    View details for PubMedID 19392385

  • Mott insulator phases and first-order melting in Bi2Sr2CaCu2O8+delta crystals with periodic surface holes PHYSICAL REVIEW B Goldberg, S., Segev, Y., Myasoedov, Y., Gutman, I., Avraham, N., Rappaport, M., Zeldov, E., Tamegai, T., Hicks, C. W., Moler, K. A. 2009; 79 (6)
  • Limits on the Superconducting Order Parameter in NdFeAsO1-xFy from Scanning SQUID Microscopy JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Hicks, C. W., Lippman, T. M., Huber, M. E., Ren, Z., Yang, J., Zhao, Z., Moler, K. A. 2009; 78 (1)
  • Mechanics of individual isolated vortices in a cuprate superconductor NATURE PHYSICS Auslaender, O. M., Luan, L., Straver, E. W., Hoffman, J. E., Koshnick, N. C., Zeldov, E., Bonn, D. A., Liang, R., Hardy, W. N., Moler, K. A. 2009; 5 (1): 35-39

    View details for DOI 10.1038/NPHYS1127

    View details for Web of Science ID 000262638900015

  • A terraced scanning superconducting quantum interference device susceptometer with submicron pickup loops APPLIED PHYSICS LETTERS Koshnick, N. C., Huber, M. E., Bert, J. A., Hicks, C. W., Large, J., Edwards, H., Moler, K. A. 2008; 93 (24)

    View details for DOI 10.1063/1.3046098

    View details for Web of Science ID 000261896400054

  • Scanning SQUID microscopy on polycrystalline SmFeAsO0.85 and NdFeAsO0.94F0.06 JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Hicks, C. W., Lippman, T. M., Moler, K. A., Huber, M. E., Ren, Z., Zhao, Z. 2008; 77: 87-90
  • Controlled manipulation of individual vortices in a superconductor APPLIED PHYSICS LETTERS Straver, E. W., Hoffman, J. E., Auslaender, O. M., Rugar, D., Moler, K. A. 2008; 93 (17)

    View details for DOI 10.1063/1.3000963

    View details for Web of Science ID 000260571800064

  • Gradiometric micro-SQUID susceptometer for scanning measurements of mesoscopic samples REVIEW OF SCIENTIFIC INSTRUMENTS Huber, M. E., Koshnick, N. C., Bluhm, H., Archuleta, L. J., Azua, T., Bjornsson, P. G., Gardner, B. W., Halloran, S. T., Lucero, E. A., Moler, K. A. 2008; 79 (5)

    Abstract

    We have fabricated and characterized micro-SQUID susceptometers for use in low-temperature scanning probe microscopy systems. The design features the following: a 4.6 mum diameter pickup loop; an integrated field coil to apply a local field to the sample; an additional counterwound pickup-loop/field-coil pair to cancel the background signal from the applied field in the absence of the sample; modulation coils to allow setting the SQUID at its optimum bias point (independent of the applied field), and shielding and symmetry that minimizes coupling of magnetic fields into the leads and body of the SQUID. We use a SQUID series array preamplifier to obtain a system bandwidth of 1 MHz. The flux noise at 125 mK is approximately 0.25 mu Phi 0/ sqrt Hz above 10 kHz, with a value of 2.5 mu Phi 0/ sqrt Hz at 10 Hz. The nominal sensitivity to electron spins located at the center of the pickup loop is approximately 200 muB/ sqrt Hz above 10 kHz, in the white-noise frequency region.

    View details for DOI 10.1063/1.2932341

    View details for Web of Science ID 000256305400019

    View details for PubMedID 18513072

  • Two-dimensional vortex behavior in highly underdoped YBa2Cu3O6+x observed by scanning Hall probe microscopy PHYSICAL REVIEW B Guikema, J. W., Bluhm, H., Bonn, D. A., Liang, R., Hardy, W. N., Moler, K. A. 2008; 77 (10)
  • Dissipative cryogenic filters with zero dc resistance REVIEW OF SCIENTIFIC INSTRUMENTS Bluhm, H., Moler, K. A. 2008; 79 (1)

    Abstract

    The authors designed, implemented, and tested cryogenic rf filters with zero dc resistance, based on wires with a superconducting core inside a resistive sheath. The superconducting core allows low frequency currents to pass with negligible dissipation. Signals above the cutoff frequency are dissipated in the resistive part due to their small skin depth. The filters consist of twisted wire pairs shielded with copper tape. Above approximately 1 GHz, the attenuation is exponential in omega, as typical for skin depth based rf filters. By using additional capacitors of 10 nF per line, an attenuation of at least 45 dB above 10 MHz can be obtained. Thus, one single filter stage kept at mixing chamber temperature in a dilution refrigerator is sufficient to attenuate room temperature black body radiation to levels corresponding to 10 mK above about 10 MHz.

    View details for DOI 10.1063/1.2835716

    View details for Web of Science ID 000252821800042

    View details for PubMedID 18248056

  • Fluctuation superconductivity in mesoscopic aluminum rings SCIENCE Koshnick, N. C., Bluhm, H., Huber, M. E., Moler, K. A. 2007; 318 (5855): 1440-1443

    Abstract

    Fluctuations are important near phase transitions, where they can be difficult to describe quantitatively. Superconductivity in mesoscopic rings is particularly intriguing because the critical temperature is an oscillatory function of magnetic field. There is an exact theory for thermal fluctuations in one-dimensional superconducting rings, which are therefore expected to be an excellent model system. We measured the susceptibility of many rings, one ring at a time, by using a scanning superconducting quantum interference device that can isolate magnetic signals that are seven orders of magnitude smaller than applied flux. We find that the fluctuation theory describes the results and that a single parameter characterizes the ways in which the fluctuations are especially important at magnetic fields where the critical temperature is suppressed.

    View details for DOI 10.1126/science.1148758

    View details for Web of Science ID 000251246100042

    View details for PubMedID 18048686

  • Moment switching in nanotube magnetic force probes NANOTECHNOLOGY Kirtley, J. R., Deng, Z., Luan, L., Yenilmez, E., Dai, H., Moler, K. A. 2007; 18 (46)

    Abstract

    Magnetic images of high density vertically recorded media using metal-coated carbon nanotube tips exhibit a doubling of the spatial frequency under some conditions (Deng et al 2004 Appl. Phys. Lett. 85 6263). Here we demonstrate that this spatial frequency doubling is due to the switching of the moment direction of the nanotube tip. This results in a signal which is proportional to the absolute value of the signal normally observed in MFM. Our modeling indicates that a significant fraction of the tip volume is involved in the observed switching, and that it should be possible to image high bit densities with nanotube magnetic force sensors.

    View details for DOI 10.1088/0957-4484/18/46/465506

    View details for Web of Science ID 000250200600013

    View details for PubMedID 21730480

  • Upper limit on spontaneous supercurrents in Sr2RuO4 PHYSICAL REVIEW B Kirtley, J. R., Kallin, C., Hicks, C. W., Kim, E., Liu, Y., Moler, K. A., Maeno, Y., Nelson, K. D. 2007; 76 (1)
  • Enhanced current flow through meandering grain boundaries in YBa2Cu3O7-delta films APPLIED PHYSICS LETTERS Dinner, R. B., Moler, K. A., Beasley, M. R., Feldmann, D. M. 2007; 90 (21)

    View details for DOI 10.1063/1.2740610

    View details for Web of Science ID 000246775900048

  • Imaging ac losses in superconducting films via scanning Hall probe microscopy PHYSICAL REVIEW B Dinner, R. B., Moler, K. A., Feldmann, D. M., Beasley, M. R. 2007; 75 (14)
  • Noise characteristics of 100 nm scale GaAs/AlxGa1-xAs scanning Hall probes APPLIED PHYSICS LETTERS Hicks, C. W., Luan, L., Moler, K. A., Zeldov, E., Shtrikman, H. 2007; 90 (13)

    View details for DOI 10.1063/1.2717565

    View details for Web of Science ID 000245317100115

  • Magnetic response of mesoscopic superconducting rings with two order parameters PHYSICAL REVIEW LETTERS Bluhm, H., Koshnick, N. C., Huber, M. E., Moler, K. A. 2006; 97 (23)

    Abstract

    The magnetic response and fluxoid transitions of superconducting aluminum rings of various sizes, deposited under conditions likely to generate a layered structure, show good agreement with a two-order-parameter Ginzburg-Landau model. For intermediate couplings, we find metastable states that have different phase winding numbers around the ring in each of the two order parameters. Those states, previously theoretically predicted, are analogous to fractional vortices in singly connected samples with two-order-parameter superconductivity. Larger coupling locks the relative phase so that the two order parameters are only manifest in the temperature dependence of the response. With increasing proximitization, this signature gradually disappears.

    View details for DOI 10.1103/PhysRevLett.97.237002

    View details for Web of Science ID 000242708900052

    View details for PubMedID 17280232

  • Power law resistivity behavior in 2D superconductors across the magnetic field-tuned superconductor-insulator transition EUROPHYSICS LETTERS Sambandamurthy, G., Johansson, A., Peled, E., Shahar, D., Bjoernsson, P. G., Moler, K. A. 2006; 75 (4): 611-617
  • Nanotube manipulation with focused ion beam APPLIED PHYSICS LETTERS Deng, Z. F., Yenilmez, E., Reilein, A., Leu, J., DAI, H. J., Moler, K. A. 2006; 88 (2)

    View details for DOI 10.1063/1.2161395

    View details for Web of Science ID 000234606900073

  • Scanning Hall probe imaging of ErNi2B2C PHYSICAL REVIEW B Bluhm, H., Sebastian, S. E., Guikema, J. W., Fisher, I. R., Moler, K. A. 2006; 73 (1)
  • Cryogenic scanning Hall-probe microscope with centimeter scan range and submicron resolution REVIEW OF SCIENTIFIC INSTRUMENTS Dinner, R. B., Beasley, M. R., Moler, K. A. 2005; 76 (10)

    View details for DOI 10.1063/1.2072438

    View details for Web of Science ID 000232855900013

  • Scanning magnetic imaging of Sr2RuO4 PHYSICAL REVIEW B Bjornsson, P. G., Maeno, Y., Huber, M. E., Moler, K. A. 2005; 72 (1)
  • Metal-coated carbon nanotube tips for magnetic force microscopy APPLIED PHYSICS LETTERS Deng, Z. F., Yenilmez, E., Leu, J., Hoffman, J. E., Straver, E. W., DAI, H. J., Moler, K. A. 2004; 85 (25): 6263-6265

    View details for DOI 10.1063/1.1842374

    View details for Web of Science ID 000225769000061

  • A scanning SQUID microscope in a dilution refrigerator PHYSICA B-CONDENSED MATTER Bjornsson, P. G., Huber, M. E., Moler, K. A. 2003; 329: 1491-1492
  • Vortex-antivortex annihilation in underdoped YBa2Cu3O6.354 PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS Gardner, B. W., Wynn, J. C., Bonn, D. A., Liang, R. X., Hardy, W. N., Moler, K. A. 2003; 388: 725-726
  • Preparation and characterization of homogeneous YBCO single crystals with doping level near the SC-AFM boundary PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS Liang, R., Bonn, D. A., Hardy, W. N., Wynn, J. C., Moler, K. A., Lu, L., LaRochelle, S., Zhou, L., Greven, M., Lurio, L., Mochrie, S. G. 2002; 383 (1-2): 1-7
  • Manipulation of single vortices in YBa2Cu3O6.354 with a locally applied magnetic field APPLIED PHYSICS LETTERS Gardner, B. W., Wynn, J. C., Bonn, D. A., Liang, R. X., Hardy, W. N., Kirtley, J. R., Kogan, V. G., Moler, K. A. 2002; 80 (6): 1010-1012
  • A limit on spin-charge separation in high-T-c superconductors from the absence of a vortex-memory effect NATURE Bonn, D. A., Wynn, J. C., Gardner, B. W., Lin, Y. J., Liang, R., Hardy, W. N., Kirtley, J. R., Moler, K. A. 2001; 414 (6866): 887-889

    Abstract

    There is a long-standing debate about whether spin-charge separation is the root cause of the peculiar normal-state properties and high superconducting transition temperatures of the high-Tc materials. In the proposed state of matter, the elementary excitations are not electron-like, as in conventional metals, but rather the electron 'fractionalizes' to give excitations that are chargeless spin-1/2 fermions (spinons) and charge +e bosons (chargons). Although spin-charge separation has been well established in one dimension, the theoretical situation for two dimensions is controversial and experimental evidence for it in the high-Tc materials is indirect. A model with sharp experimental tests for a particular type of separation in two dimensions has recently been proposed. Here we report the results of those experimental tests, placing a conservative upper limit of 190 K on the energy of the proposed topological defects known as visons. There is still debate about the extent to which this experiment can settle the issue of spin-charge separation in the high-Tc copper oxides, because some forms of the separation are able to avoid the need for visons. But at least one class of theories that all predict a vortex-memory effect now are unlikely models for the copper oxides.

    View details for Web of Science ID 000172813300039

    View details for PubMedID 11780056

  • Limits on spin-charge separation from h/2e fluxoids in very underdoped YBa2Cu3O6+x PHYSICAL REVIEW LETTERS Wynn, J. C., Bonn, D. A., Gardner, B. W., Lin, Y. J., Liang, R. X., Hardy, W. N., Kirtley, J. R., Moler, K. A. 2001; 87 (19)

    Abstract

    Magnetic flux in superconductors is usually quantized in units of h/2e. Here we report scanning SQUID and scanning Hall probe studies of single fluxoids in high purity YBa2Cu3O6.35 crystals (T(c) less, similar 13 K), extending flux quantization studies to a region of the cuprate phase diagram where the superfluid density is sufficiently low that novel behavior has been predicted. Some scenarios in which superconductivity results from spin-charge separation predict h/e fluxoids in materials with low superfluid density. Our observations of only h/2e fluxoids set limits on these theories.

    View details for DOI 10.1103/PhysRevLett.87.197002

    View details for Web of Science ID 000172027200047

    View details for PubMedID 11690445

  • Scanning superconducting quantum interference device microscope in a dilution refrigerator REVIEW OF SCIENTIFIC INSTRUMENTS Bjornsson, P. G., Gardner, B. W., Kirtley, J. R., Moler, K. A. 2001; 72 (11): 4153-4158
  • Scanning superconducting quantum interference device susceptometry REVIEW OF SCIENTIFIC INSTRUMENTS Gardner, B. W., Wynn, J. C., Bjornsson, P. G., Straver, E. W., Moler, K. A., Kirtley, J. R., Ketchen, M. B. 2001; 72 (5): 2361-2364
  • Images of interlayer Josephson vortices in single-layer cuprates PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS Moler, K. A., Kirtley, J. R., Liang, R. X., Bonn, D. A., Hardy, W. N., Williams, J. M., Schlueter, J. A., Hinks, D., Villard, G., Maignan, A., Nohara, M., Takagi, H. 2000; 341: 977-980
  • Temperature dependence of the half-integer magnetic flux quantum SCIENCE Kirtley, J. R., Tsuei, C. C., Moler, K. A. 1999; 285 (5432): 1373-1375
  • Variable sample temperature scanning superconducting quantum interference device microscope APPLIED PHYSICS LETTERS Kirtley, J. R., Tsuei, C. C., Moler, K. A., Kogan, V. G., Clem, J. R., Turberfield, A. J. 1999; 74 (26): 4011-4013
  • Inhomogeneous interlayer Josephson coupling in kappa-(BEDT-TTF)(2)Cu(NCS)(2) JOURNAL OF PHYSICS-CONDENSED MATTER Kirtley, J. R., Moler, K. A., Schlueter, J. A., Williams, J. M. 1999; 11 (8): 2007-2016
  • Magnetic field of an in-plane vortex outside a layered superconductor PHYSICAL REVIEW B Kirtley, J. R., Kogan, V. G., Clem, J. R., Moler, K. A. 1999; 59 (6): 4343-4348
  • Temperature Dependence of the Half-Integer Magnetic Flux Quantum. Science (New York, N.Y.) Kirtley, J. R., Tsuei, C. C., Moler, K. A. 1999; 285 (5432): 1373-1375

    Abstract

    The temperature dependence of the half-integer magnetic flux quantum effect in thin-film tricrystal samples of the high-critical-temperature cuprate superconductor YBa(2)Cu(3)O(7-delta) was measured and found to persist from a temperature of 0.5 kelvin through a critical temperature of about 90 kelvin, with no change in total flux. This result implies that d-wave symmetry pairing predominates in this cuprate, with a small component of time-reversal symmetry breaking, if any, over the entire temperature range.

    View details for PubMedID 10464089

  • The influence of grain boundary roughness on tricrystal symmetry tests SYMMETRY AND PAIRING IN SUPERCONDUCTORS Kirtley, J. R., Tsuei, C. C., Moler, K. A., Mannhart, J., Hilgenkamp, H. 1999; 63: 337-346
  • c-axis penetration depth in single crystal La2-xSrxCuO4 HIGH TEMPERATURE SUPERCONDUCTIVITY Kirtley, J. R., Moler, K. A., Nohara, M., Takagi, H. 1999; 483: 247-252
  • Global and local measures of the intrinsic Josephson coupling in Tl2Ba2CuO6 as a test of the interlayer tunnelling model NATURE Tsvetkov, A. A., van der Marel, D., Moler, K. A., Kirtley, J. R., de Boer, J. L., Meetsma, A., Ren, Z. F., Koleshnikov, N., Dulic, D., Damascelli, A., Gruninger, M., Schutzmann, J., van der Eb, J. W., Somal, H. S., Wang, J. H. 1998; 395 (6700): 360-362
  • c-Axis penetration depth of Hg-1201 single crystals PHYSICAL REVIEW LETTERS Kirtley, J. R., Moler, K. A., Villard, G., Maignan, A. 1998; 81 (10): 2140-2143
  • Images of interlayer Josephson vortices in Tl2Ba2CuO6+delta SCIENCE Moler, K. A., Kirtley, J. R., Hinks, D. G., Li, T. W., Xu, M. 1998; 279 (5354): 1193-1196
  • Flux quantization experiments in cuprate superconductors GAP SYMMETRY AND FLUCTUATIONS IN HIGH-T(C) SUPERCONDUCTORS Kirtley, J. R., Tsuei, C. C., Moler, K. A. 1998; 371: 537-556
  • Spontaneous flux and magnetic-interference patterns in O-pi Josephson junctions PHYSICAL REVIEW B Kirtley, J. R., Moler, K. A., Scalapino, D. J. 1997; 56 (2): 886-891
  • Influence of d(x2-y2) symmetry on device applications of high-T-c grain boundary junctions IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY Hilgenkamp, H., Mannhart, J., Mayer, B., Gerber, C., Kirtley, J. R., Moler, K. A. 1997; 7 (2): 3670-3673
  • Scanning SQUID microscopy of sparsely twinned YBa2Cu3O7-delta PHYSICAL REVIEW B Moler, K. A., Kirtley, J. R., Liang, R. X., Bonn, D., Hardy, W. N. 1997; 55 (18): 12753-12758
  • Specific heat of YBa2Cu3O7-delta PHYSICAL REVIEW B Moler, K. A., Sisson, D. L., Urbach, J. S., Beasley, M. R., Kapitulnik, A., BAAR, D. J., Liang, R. X., Hardy, W. N. 1997; 55 (6): 3954-3965
  • Generation of magnetic flux by single grain boundaries of YBa2Cu3O7-x PHYSICAL REVIEW LETTERS Mannhart, J., Hilgenkamp, H., Mayer, B., Gerber, C., Kirtley, J. R., Moler, K. A., Sigrist, M. 1996; 77 (13): 2782-2785
  • Basic aspects of high-T-c grain boundary devices JOURNAL DE PHYSIQUE IV Mannhart, J., Hilgenkamp, H., Mayer, B., Gerber, C., Kirtley, J. R., Moler, K. A., Sigrist, M. 1996; 6 (C3): 329-334
  • Direct imaging of integer and half-integer Josephson vortices in high-T-c grain boundaries PHYSICAL REVIEW LETTERS Kirtley, J. R., Tsuei, C. C., Rupp, M., Sun, J. Z., YUJAHNES, L. S., Gupta, A., Ketchen, M. B., Moler, K. A., Bhushan, M. 1996; 76 (8): 1336-1339
  • Scanning SQUID microscope tests of the symmetry of the high-T-c gap CZECHOSLOVAK JOURNAL OF PHYSICS Kirtley, J. R., Tsuei, C. C., Moler, K. A., Sun, J. Z., Gupta, A., Ren, Z. F., Wang, J. H., Li, Z. Z., Raffy, H., Mannhart, J., Hilgenkamp, H., Mayer, B., Gerber, C. 1996; 46: 3169-3176
  • Specific heat of YBa2Cu3O7-delta single crystals: Implications for the vortex structure Moler, K. A., Kapitulnik, A., BAAR, D. J., Liang, R. X., Hardy, W. N. PERGAMON-ELSEVIER SCIENCE LTD. 1995: 1899-1904
  • MAGNETIC-FIELD DEPENDENCE OF THE DENSITY-OF-STATES OF YBA2CU3O6.95 - IMPLICATIONS FOR THE VORTEX STRUCTURE Moler, K. A., BAAR, D. J., Liang, R. X., Hardy, W. N., Kapitulnik, A. SPRINGER/PLENUM PUBLISHERS. 1995: 571-574
  • PROPOSED THERMODYNAMIC METHOD TO DETERMINE THE VORTEX MASS IN LAYERED SUPERCONDUCTORS JOURNAL OF LOW TEMPERATURE PHYSICS Moler, K. A., Fetter, A. L., Kapitulnik, A. 1995; 100 (3-4): 185-193
  • NORMAL-MODES AND SPECIFIC-HEAT OF AN UNDAMPED 3-DIMENSIONAL LATTICE OF PANCAKE VORTICES IN THIN SUPERCONDUCTING MULTILAYERS PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS Fetter, A. L., Kapitulnik, A., Moler, K. A. 1994; 235: 1777-1778
  • MAGNETIC-FIELD DEPENDENCE OF THE ELECTRONIC SPECIFIC-HEAT IN YBA2CU3O6.95 SINGLE-CRYSTALS PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS Moler, K. A., BAAR, D. J., Urbach, J. S., Liang, R. X., Hardy, W. N., Kapitulnik, A. 1994; 235: 1775-1776
  • MAGNETIC-FIELD DEPENDENCE OF THE DENSITY-OF-STATES OF YBA2CU3O6.95 AS DETERMINED FROM THE SPECIFIC-HEAT PHYSICAL REVIEW LETTERS Moler, K. A., BAAR, D. J., Urbach, J. S., Liang, R. X., Hardy, W. N., Kapitulnik, A. 1994; 73 (20): 2744-2747
  • THEORETICAL-ANALYSIS OF VELOCITY-SELECTIVE RAMAN TRANSITIONS PHYSICAL REVIEW A Moler, K., Weiss, D. S., Kasevich, M., Chu, S. 1992; 45 (1): 342-348
  • ATOMIC VELOCITY SELECTION USING STIMULATED RAMAN TRANSITIONS PHYSICAL REVIEW LETTERS Kasevich, M., Weiss, D. S., Riis, E., Moler, K., Kasapi, S., Chu, S. 1991; 66 (18): 2297-2300
  • APPLICATIONS OF LASER COOLING AND TRAPPING ATOMIC PHYSICS 12 Kasevich, M., Moler, K., Riis, E., SUNDERMAN, E., Weiss, D., Chu, S. 1991; 233: 47-57
  • ATOM FUNNEL FOR THE PRODUCTION OF A SLOW, HIGH-DENSITY ATOMIC-BEAM PHYSICAL REVIEW LETTERS Riis, E., Weiss, D. S., Moler, K. A., Chu, S. 1990; 64 (14): 1658-1661

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