Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C41: Superconductivity: Phase Transition & Related |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Mike Osofsky, Naval Research Laboratory Room: 388 |
Monday, March 13, 2017 2:30PM - 2:42PM |
C41.00001: Microwave Spectroscopic Investigation of the Superconductor Insulator Transition in a Strongly Disordered Superconductor Youcheng Wang, Idan Tamir, Dan Shahar, N. P. Armitage Superconductor insulator transitions (SIT) driven by disorder or perpendicular magnetic field in 2D disordered superconductor thin films is a protypical example of a quantum phase transition. There can be a field-tuned transition, as $T\rightarrow0$, from vortex glass (superconductor) to Cooper pair glass (insulator) wherein vortices Bose condense and delocalize. Here we measure the complex dynamical response within a broadband of frequencies ($50 MHz-\sim10 GHz$) of a strongly disordered $InO_x$ thin film across its SIT using Corbino microwave spectroscopy. We report the frequency dependence of complex conductance and the critical behavior of superfluid density and fluctuation rate, along with the temperature and field dependence of DC sheet resistance. [Preview Abstract] |
Monday, March 13, 2017 2:42PM - 2:54PM |
C41.00002: Unusual vortex dynamics and phase transitions in mesoscopic superconducting islands Rita Garrido Menacho, Malcolm Durkin, Nadya Mason Granular mesoscopic niobium (Nb) islands provide a stage for strong confinement and pinning effects for vortex dynamics. We performed magnetotransport measurements on single Nb islands with varying diameters. We observed non-periodic oscillations in magnetoresistance along the superconducting transition which suggest non-trivial vortex configurations. Furthermore, we found strong indications of a quantum phase transition as a function of diameter. At large diameters (above 2 um) we observed an apparent crossing point in the magnetoresistance at the critical field (B$_{c}$) coupled with a magnetoresistance peak when the field is increased further. These signatures suggest a superconductor-to-metal transition and a quantum critical point at B$_{c}$, at resistances far below the quantum of resistance R$_{Q}$. [Preview Abstract] |
Monday, March 13, 2017 2:54PM - 3:06PM |
C41.00003: Superconductivity in TaSe$_2$ compounds doped with Pt Wenkai Zheng, Qiurun Zhang, Daniel Rhodes, Yuche Chiu, Rico Schoenemann, Qiong Zhou, Shahriar Memaran, Thomas Martin, Julia Chan, Luis Balicas Here, we report the observation of superconductivity in Pt doped TaSe$_2$ with Pt doping levels ranging from 0.1\% to 5\%. TaSe$_2$ displays a dome of superconductivity that is dependent upon the Pt content with some evidence for quantum criticality associated with the suppression of charge density wave phase observed around 110 K. Pt doping is able to induce superconductivity in TaSe$_2$ with a maximum superconducting critical temperature of 2.5 K. We observe a sizeable anisotropy in upper critical fields between fields applied along planar and the inter-planar directions and it also depend on the doping levels. [Preview Abstract] |
Monday, March 13, 2017 3:06PM - 3:18PM |
C41.00004: The Observability of Quantum Pinch Effect in Semiconducting Quantum Wires Manvir Kushwaha We report on a two-component, cylindrical, quasi-one-dimensional quantum plasma subjected to a {\em radial} confining harmonic potential and an applied magnetic field in the symmetric gauge. It is demonstrated that such a system as can be realized in semiconducting quantum wires offers an excellent medium for observing the quantum pinch effect at low temperatures. An exact analytical solution of the problem allows us to make significant observations: surprisingly, in contrast to the classical pinch effect, the particle density as well as the current density display a {\em determinable} maximum before attaining a minimum at the surface of the quantum wire. The effect will persist as long as the equilibrium pair density is sustained. Therefore, the technological promise that emerges is the route to the precise electronic devices that will control the particle beams at the nanoscale.[See, e.g., M.S. Kushwaha, Appl. Phys. Lett. {\bf 103}, 173116 (2013)] [Preview Abstract] |
Monday, March 13, 2017 3:18PM - 3:30PM |
C41.00005: Possible existence of a filamentary state in type-II superconductors V. Kozhevnikov, A.-M. Valente-Feliciano, P. Curran, A. Suter, H. Liu, G. Richter, E. Morenzoni, S. Bending, C. Van Haesendonck The standard interpretation of the phase diagram of type-II superconductors was developed in 1960s and has since been considered a well-established part of classical superconductivity. However, upon closer examination a number of fundamental issues arise that leads one to question this standard picture. To address these issues we studied equilibrium properties of Nb samples near and above the upper critical field $H_{c2}$ in parallel and perpendicular fields. The samples were very high quality Nb films and single crystal discs with the Ginzburg-Landau parameters 0.8 and 1.3, respectively. A range of complementary measurements have been performed, which include dc magnetometry, electrical transport, muSR and scanning Hall-probe microscopy. Contrarily to the standard scenario, we observed that a superconducting phase is present in the sample bulk above $H_{c2}$ and the field $H_{c3}$ is the same in both parallel and perpendicular fields. Our findings suggest that above $H_{c2}$ the superconducting phase forms filaments parallel to the field regardless on the field orientation. Near $H_{c2}$ the filaments preserve the hexagonal structure of the preceding vortex lattice of the mixed state and the filament density continuously falls to zero at $H_{c3}$. [Preview Abstract] |
Monday, March 13, 2017 3:30PM - 3:42PM |
C41.00006: Effects of magnetic impurities on the Cooper Pair Insulator state Xue Zhang, James Joy, J.M. Xu, James Valles Superconductivity can be destroyed by adding magnetic impurities that produce time-reversal symmetry breaking electron scattering. In contrast to non-magnetic impurities, a tiny concentration of magnetic impurities can reduce the superconducting gap significantly. In our lab, we are investigating the Cooper pair insulator state that forms at the superconductor to insulator transition in metal films deposited onto nanostructured substrates. This bose insulator state exhibits activated transport and a giant magnetoresistance peak similar to ones observed in other thin film systems. We are investigating how this novel insulating state responds to the addition of magnetic impurities. One of the goals is to gain insights into the microscopic origin of the transport activation energy. In this talk, I will present our latest results on how the transport properties of the Cooper pair insulator phase have drastically changed with addition of magnetic impurities. [Preview Abstract] |
Monday, March 13, 2017 3:42PM - 3:54PM |
C41.00007: The influence of domain walls in the incommensurate charge density wave state of Cu intercalated 1$T$-TiSe$_{\mathrm{2}}$ Shichao Yan, Davide Iaia, Emilia Morosan, Eduardo Fradkin, Peter Abbamonte, Vidya Madhavan We report a low-temperature scanning tunneling microscopy study of the charge density wave (CDW) order in 1$T$-TiSe$_{\mathrm{2}}$ and Cu$_{\mathrm{0.08}}$TiSe$_{\mathrm{2}}$. In 1$T$-TiSe$_{\mathrm{2}}$ we observe a long-range coherent commensurate CDW (C-CDW) order. In contrast, Cu$_{\mathrm{0.08}}$TiSe$_{\mathrm{2}}$ displays an incommensurate CDW (I-CDW) phase with localized C-CDW domains separated by domain walls. Density of states measurements indicate that the domain walls host an extra population of fermions near the Fermi level which may play a critical role in the emergence of superconductivity in this system. Fourier transform scanning tunneling spectroscopy studies show that the dominant mechanism for CDW formation in the I-CDW phase is electron-phonon coupling. [Preview Abstract] |
Monday, March 13, 2017 3:54PM - 4:06PM |
C41.00008: Emergent superconductivity in tricolor Kondo superlattices Yuichi Kasahara, Y. Naritsuka, T. Ishii, S. Miyake, T. Terashima, Y. Matsuda, Y. Tokiwa, M. Shimozawa, T. Shibauchi Spin-orbit interactions, together with inversion symmetry breaking, dramatically affect the superconductivity, leading to several exotic phenomena. In the presence of strong electron correlations, such phenomena are predicted to be more pronounced in two-dimensional system. Here, we report on the observation of superconductivity in tricolor Kondo superlattices with an asymmetric stacking sequence. In such superlattices, superconducting state emerges from strongly correlated heavy electrons confined within a two-dimensional Kondo lattice with asymmetric potential gradient. We found that angular and temperature dependences of upper critical fields show distinct behavior from those in centrosymmetric systems, suggesting suppression of the Pauli pair-breaking effect due to strong spin-orbit coupling associated with global inversion symmetry breaking. We will also discuss the possibility of helical or stripe phase with inhomogeneous order parameter in the tricolor Kondo superlattices. [Preview Abstract] |
Monday, March 13, 2017 4:06PM - 4:18PM |
C41.00009: Spin-orbit coupled superconductivity at the interface of LaAlO3/SrTiO3 Wei-Li Lee, Chi-Sheng Li, Akhilesh Singh, Ming-Yuan Song, Ming-Wen Chu By using oxide MBE technique, we have grown few monolayers of epitaxial LaAlO$_3$ (LAO) on TiO2 terminated SrTiO$_3$ (STO) substrates, which shows an interface superconductivity below about 0.3 K. Scanning tunneling electron microscope images revealed a sharp atomic interface between LAO and STO in our LAO/STO samples. By fabricating a back gate electrode via the STO substrate, the superconductor‐insulator transition was observed by applying gate voltages on a macroscopic size of the two‐dimensional electron liquid (2DEL) at the interface of LAO/STO. From the superconducting critical field anisotropy measurements, a sizable spin‐orbit coupling (SOC) is likely to present in the superconducting phase, where the upper limit of the SOC strength can be largely tuned by gate voltages. In addition, magneto‐transport anomaly was found when depleting the electron density and thus driving the 2DEL into insulating phase, suggesting an inhomogeneous density distribution and also a possible multi‐band conduction in the 2DEL. [Preview Abstract] |
Monday, March 13, 2017 4:18PM - 4:30PM |
C41.00010: Thickness induced superconductor-insulator transition in epitaxial La-Sr-Cu-O Han-Byul Jang, Ji Soo Lim, Chan-Ho Yang For many years, the superconductor-to-insulator transition (SIT) is studied by controlling external magnetic field, gating voltage, and hydrostatic pressure. In particular, for thin film systems, film thickness is also a candidate parameter by changing the dimensionality of system. We investigate SIT for the thickness dependent epitaxial La$_{\mathrm{1.85}}$Sr$_{\mathrm{0.15}}$CuO$_{\mathrm{4\thinspace }}$thin films on LaAlO$_{\mathrm{3\thinspace }}$with various perspectives. Electronic transport measurement shows thickness dependent $T_{\mathrm{c\thinspace }}$and SIT occurs at a critical thickness of \textasciitilde 15 nm. By using transmission electronic microscopy imaging, it directly supports high quality of the epitaxial films with minimizing dislocations in the atomic resolution. X-ray diffraction and reciprocal space map represent that $c$-axis and in-plane lattice parameters exhibit no significant change and fully strained on substrate for all thicknesses. In addition, x-ray photoemission spectroscopy for O 1s and Cu 2p core level spectra also reveals a similar electronic structure irrelevant to the thickness. We will discuss possible mechanisms for the observed SIT. [Preview Abstract] |
Monday, March 13, 2017 4:30PM - 4:42PM |
C41.00011: Quantum Monte Carlo Study of Superconductor-Insulator Transition and BCS-BEC crossover in a two-band system Tamaghna Hazra, Richard Scalettar, Nandini Trivedi, Mohit Randeria A direct transition from an insulator to a superconductor (SC) forces us to re-examine our conventional understanding of superconductivity as a Fermi surface instability. We have recently introduced a simple, disorder-free, two-band fermionic model to address this issue. We found that [1] the route from fermionic insulator to SC proceeds through a crossover to a Bose insulator, with low energy charge $2e$ excitations, followed by a phase transition to a BEC of these bosons, and finally a crossover to a BCS SC with an underlying Fermi surface. Using sign-problem free Quantum Monte Carlo simulations, we establish that the insulator near the SC-insulator transition (SIT) is characterized by a two-particle gap which drops below the one-particle gap $E_g$ and goes soft at the SIT while $E_g$ remains finite. In the SC, characterized by finite superfluid stiffness and compressibility, this naturally leads to a pairing pseudogap above $T_c$. We study how this BEC SC crosses over to a two-band BCS SC at half-filling, which is relevant for compensated semi-metals. Our work unequivocally establishes that the SIT is from a Bose insulator to a BEC, and provides insights into the BCS-BEC crossover in multi-band systems away from weak coupling. [1] Y. L. Loh et al, Phys. Rev. X 6, 021029(2016) [Preview Abstract] |
Monday, March 13, 2017 4:42PM - 4:54PM |
C41.00012: Quantum Monte Carlo study of the superconductor-insulator transition in the dual vortex representation Hasan Khan, Snir Gazit, Mohit Randeria, Nandini Trivedi The superconductor-insulator transition (SIT) in two dimensions is a paradigm for quantum criticality that has been observed experimentally in Josephson junction arrays, superconducting thin films, and cold atoms trapped in an optical lattice. The conventional picture of the transition is in terms of the condensation of bosonic degrees of freedom (Cooper pairs in superconductors). Interestingly, the transition has a dual description, where the insulating phase is a Bose condensate of vortices. We study the SIT numerically by means of a large-scale quantum Monte Carlo (QMC) simulation in the vortex representation. This provides direct access to both the boson and vortex degrees of freedom and allows us to numerically test the duality and quantify deviations from self-duality. Our main focus is on critical properties such as the vortex and the boson phase stiffness. We compare our results to previous studies in the bosonic representation. [Preview Abstract] |
Monday, March 13, 2017 4:54PM - 5:06PM |
C41.00013: Universal Lower Limit on Vortex Creep in Superconductors Serena Eley, Masashi Miura, Boris Maiorov, Leonardo Civale In high-temperature superconductors, creep (the rate of thermally-activated vortex motion, $\textit{S}$) considerably limits the current carrying capacity. The magnitude of $\textit{S}$ is thought to somehow positively correlate with the Ginzburg number ($\textit{Gi}$), which depends on the critical temperature ($\textit{T}_c$) and material-specific length scales. Early measurements of $\textit{S}$ in iron-based superconductors unveiled rates comparable to YBa$_2$Cu$_3$O$_{7-\delta}$, which was puzzling given that $\textit{Gi}$ is orders of magnitude lower in iron-based superconductors. Here, we report very slow creep in BaFe$_2$(As$_{0.67}$P$_{0.33}$)$_2$ films and evince the efficacy of BaZrO$_3$ inclusions in reducing $\textit{S}$ at high fields. We propose that there is a universal minimum realizable $S \sim Gi^{\frac{1}{2}}(\frac{T}{T_c})$ , and show that it has been achieved in our films, a few other superconductors, and violated by none. This hard constraint has two broad implications: first, the creep problem in high-$\textit{T}_c$ superconductors cannot be fully eliminated and there is a limit to how much it can be ameliorated, and secondly, we can confidently predict that any yet-to-be-discovered high-$\textit{T}_c$ superconductor will have fast creep. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700