Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E08: Lower Temperature Superconductors |
Hide Abstracts |
Sponsoring Units: DCMP DMP Chair: Lilia Boeri, Sapienza University of Rome Room: BCEC 150 |
Tuesday, March 5, 2019 8:00AM - 8:12AM |
E08.00001: Nanocalorimetric Evidence for Nematic Superconductivity in Sr0.1Bi2Se3 Kristin Willa, Roland Willa, Kok Wee Song, Genda Gu, Ruidan Zhong, John A. Schneeloch, Alexei E Koshelev, Wai-Kwong Kwok, Ulrich Welp Spontaneous rotational-symmetry breaking in the superconducting state of doped Bi2Se3 has attracted significant attention as an indicator for topological superconductivity. High-resolution calorimetry of single-crystal Sr0.1Bi2Se3 provides unequivocal evidence of a twofold rotational symmetry in the superconducting gap by a bulk thermodynamic probe, a fingerprint of nematic superconductivity. The extremely small specific heat anomaly resolved with our high-sensitivity technique is consistent with the material's low carrier concentration proving bulk superconductivity. The large basal-plane anisotropy of Hc2 is attributed to a nematic phase of a two-component topological gap structure η = (η1, η2) and caused by a symmetry-breaking energy term δ(|η1|2 - (|η2|2) Tc. A quantitative analysis of our data excludes more conventional sources of this two-fold anisotropy and provides the first estimate for the symmetry-breaking strength δ ~ 0.1. |
Tuesday, March 5, 2019 8:12AM - 8:24AM |
E08.00002: μSR and Magnetometry Study of the Type I Superconductor BeAu James Beare, Matthew Nugent, Murray N Wilson, Eteri Svanidze, Yipeng Cai, Alfred Amon, Andreas Leithe-Jasper, Zizhou Gong, Zurab Guguchia, Yuri Grin, Yasutomo J Uemura, Graeme Luke We present Muon Spin Rotation and Relaxation (μSR) measurements as well as demagnetisation corrected magnetometry measurements on polycrystalline samples of the noncentrosymmetric superconductor BeAu. From μSR measurements in a transverse field we find that BeAu is a rare Type I superconducting alloy. To account for demagnetising effects in magnetometry measurements we produced an ellipsoidal sample for which we could calculate the demagnetising factor and found results comparable with our µSR measurments. From both sets of measurements we have constructed a phase diagram from 30 mK to Tc ≈ 3.25K. We also studied the effect of hydrostatic pressure and find that 450 MPa decreases Tc by 44 mK, comparable to the change seen in several elemental type I superconductors. |
Tuesday, March 5, 2019 8:24AM - 8:36AM |
E08.00003: Direct evidence of multi-band superconductivity in Mo8Ga41 Anshu Sirohi, Surabhi Saha, Prakriti Neha, Shekhar Das, Satyabrata Patnaik, Tanmoy Das, Goutam Sheet Mo8Ga41, a member of the family of endohedral gallide cluster compounds shows superconductivity with relatively large Tc of 9.8 K as compare to the other members in this family. In order to study the superconducting phase of Mo8Ga41 a number of experiments have been employed and it was shown that this compound manifests unusually high electron-phonon coupling leading to a large △/kBTc ratio and an indication of multi-gap superconductivity was also found. In this talk, from the direct measurement of the superconducting energy gap measured by Scanning Tunneling Spectroscopy (STS), I will show that Mo8Ga41 is a two-gap superconductor like MgB2 with the superconducting energy gaps of magnitude 0.85 meV and 1.6 meV respectively. Evolution of superconducting energy gaps with temperature and magnetic field demonstrates the conventional nature of both of the gaps as per the BCS prediction. In addition, through the band structure calculations, we have also identified the bands responsible for the two respective gaps and also shows that only two specific Mo sites in an unit cell contribute to superconductivity. Magnetic field dependent STS experiments further suggest that the interband coupling is weak in Mo8Ga41, as in case of MgB2. |
Tuesday, March 5, 2019 8:36AM - 8:48AM |
E08.00004: Evidence of a structural quantum critical point in (CaxSr1-x)3Rh4Sn13 from a lattice dynamics study Yiu Wing Cheung, Yajian Hu, Masaki Imai, Yasuaki Tanioku, Hibiki Kanagawa, Joichi Murakawa, Kodai Moriyama, Wei Zhang, Kwing To Lai, Kazuyoshi Yoshimura, Malte Grosche, Koji Kaneko, Satoshi Tsutsui, Swee Kuan Goh The nonmagnetic quasiskutterudite (CaxSr1-x)3Rh4Sn13 represents a precious system to explore the interplay between structural instabilities and superconductivity by tuning the Ca concentration x [1-3]. We performed inelastic x-ray scattering to probe the phonon spectrum of (CaxSr1-x)3Rh4Sn13 for various calcium contents. We detected a complete phonon softening at the M point when approaching the structural transition temperature from above. Intriguingly, at x = 0.85, the energy squared of the soft mode at M extrapolates to zero at (-5.7 ± 7.7) K, providing the first compelling microscopic evidence of a structural quantum critical point (QCP) in (CaxSr1-x)3Rh4Sn13. The observed phonon softening around the M point provides the essential ingredient for realizing strong-coupling superconductivity near the structural QCP [4]. |
Tuesday, March 5, 2019 8:48AM - 9:00AM |
E08.00005: Singlet superconductivity in single-crystal NiBi3 superconductor Gejian Zhao, Xinxin Gong, Pengchao Xu, Bochao Li, Zhiyu Huang, Xiaofeng Jin, Xiang-de Zhu, Tingyong Chen Verification of triplet superconductors (SCs), especially those that can carries spin angular momentum, is essential for understanding fundamental mechanism of unconventional superconductivity as well as important applications in quantum computing and spintronics. But singlet and triplet SCs have similar macroscopic properties, an ideal experiment would be to directly measure the spin states of Cooper pairs. In this work, Andreev reflection spectroscopy with unpolarized and highly spin-polarized currents has been utilized to study an intermetallic single-crystal SC NiBi3. Magnetoresistance at zero bias voltage of point contacts shows the occurrence and suppression of Andreev reflection by unpolarized and polarized current, respectively. The gap value, its symmetry and temperature dependence have been determined using an unpolarized current. The spin state in the NiBi3 sample is determined to be antiparallel using a highly spin-polarized current. The gap value 2D/kBT, gap symmetry and its temperature dependence, combined with the antiparallel spin state show that the bulk NiBi3 is a singlet s-wave superconductor. |
Tuesday, March 5, 2019 9:00AM - 9:12AM |
E08.00006: Magnesium Diboride Thin Film Cavity Fabricated by Hybrid Physical Chemical Vapor Deposition Xin Guo, Wenura K Withanage, Jay R. Paudel, Alireza Nassiri, Xiaoxing Xi Magnesium diboride (MgB2) is considered as a potential material for superconducting radio frequency cavities. MgB2 thin film fabricated on an inner surface of the Cu cavity will allow for a higher operational temperature because of the higher transition temperature of MgB2 and the high thermal conductivity of Cu. Using the hybrid physical chemical vapor deposition (HPCVD) technique, a uniform MgB2 coatings were achieved on the inner wall of the 3 GHz Cu cavity. The quality of the films were characterized on small Cu samples which were mounted at different selected locations of the cavity. Preliminary RF result for the MgB2 thin film cavity will be presented. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E08.00007: The extraordinary superconductivity of commercial niobium-titanium wire at extreme pressures Liling Sun, Jing Guo, Gongchang Lin, Shu Cai, Chuanying Xi, Changjin Zhang, Wanshuo Sun, Qiuliang Wang, Qi Wu, Yuheng Zhang, Tao Xiang, Robert Cava We report the observation of extraordinary superconductivity in a pressurized commercial niobium-titanium alloy wire. We demonstrate that its zero-resistance superconductivity persists from ambient pressure to pressures as high as 261.7 GPa, a pressure that falls within that of the outer core of the earth, establishing the record where a superconducting state continuously survives. At such high pressures the superconducting transition temperature (TC) has increased from ~9.6 K to ~19.1 K and the critical magnetic field (HC2) at 1.8 K from 15.4 T to 19 T, setting new records for both TC and HC2 among all the known transition element alloy superconductors, all, remarkably, in spite of a 45% volume shrinkage. The behavior is quite different from what is seen in copper oxide and iron pnictide superconductors, whose superconducting transition temperatures are quite sensitive to subtle changes in the lattice structure. Our results therefore not only provide fresh information on the remarkable properties of this commercial superconductor, but also pose a substantial challenge for models of a phenomenon as “well understood” as conventional electron-phonon coupled superconductivity. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E08.00008: Field-induced large resistance peak in superconducting niobium thin films deposited on surface reconstructed SrTiO3 substrate Akhilesh Singh, Tsung-Chi Wu, Uddipta Kar, Wei-Cheng Lee, Wei-Li Lee It is known that oxygen vacancies in SrTiO3(STO) can result in surface reconstructions (SR), giving rise to a metallic surface and unusual surface phonon modes. Few earlier works have demonstrated intriguing phenomena of a huge superconducting transition temperature enhancement in a monolayer FeSe on SR-STO substrate, where its intrinsic mechanism remains debatable. In this work, we constructed a phase diagram of SR-STO with surface structures of, where SR-STO samples were prepared via thermal annealing in ultra-high vacuum followed by low energy electron diffraction analysis. Thin Nb films with different thicknesses (t) were deposited on the SR-STO. The detail studies on the magnetotransport and superconducting properties of the Nb(t)/SR-STO films revealed a large positive magnetoresistance, and a pronounced resistance peak occurred near the onset of the resistive superconducting transition in the presence of a large magnetic field. Remarkably, amplitude of the resistance peaks increases with increasing fields, reaching a value of nearly 340 % of the normal state resistance at 12 T. Such resistance peaks were not observed for the control samples of Nb(t)/STO and Nb(t)/SiO2. Possible mechanisms of the large field-induced resistance peak will be discussed. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E08.00009: Effects of dimensionality and magnetic correlations on superconducting properties of MoCo thin films Tomas Polakovic, Terence Bretz-Sullivan, JOHN E. PEARSON, J Samuel Jiang, Anand Bhattacharya, Axel F Hoffmann, Goran Karapetrov, Valentyn Novosad The ability to precisely control superconducting transition within a narrow range of temperatures is crucial for many applications in cryogenic detectors. One way of achieving this is by utilizing magnetic impurities in superconductors. We present a systematic study of the effect of Co dopant on superconducting Molybdenum thin films prepared by sputtering from alloyed targets over a broad range of impurity concentrations and film thicknesses. Electric and magnetic measurements show strong dependence of the critical temperature on Co concentration, as well as presence of Kondo effect that vanishes as the film thickness is reduced. In addition to the pair-breaking effect due to magnetic impurities, we also explore the trend of TC reduction with decreasing film thickness, generally attributed to the reduction of the superconducting order parameter on the surfaces. |
Tuesday, March 5, 2019 9:48AM - 10:00AM |
E08.00010: Carrier and epitaxial strain control of superconductivity in LaO thin film Kenichi Kaminaga, Daichi Oka, Tetsuya Hasegawa, Tomoteru Fukumura We report effects of carrier density and epitaxial strain on superconductivity in rock-salt lanthanum monoxide (LaO) epitaxial thin film [1]. Electron carrier doping via introducing oxygen vacancies resulted in a dome-shaped Tc as a function of carrier density. In addition, epitaxial strain influenced significantly the Tc despite its highly symmetric rock-salt structure. Tc was raised up to 5.2 K in tensilely strained thin film on LaAlO3 substrate, in contrast with Tc of at most 4.5 K in compressive strained film on YAlO3 substrate. [1] K. Kaminaga et al., J. Am. Chem. Soc. 140, 6754 (2018). |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E08.00011: Evidence for the Berezinskii–Kosterlitz–Thouless transition in an Al nanofilm grown by molecular beam epitaxy Chi-Te Liang, Guan-Ming Su, Ankit Kumar, Chau-Shing Chang, Ching-Chen Yeh, Bi-Yi Wu, Dinesh Patel, Yen-Ting Fan, Sheng-Di Lin, Lee Chow In this work, we present experimental evidence for the Berezinskii–Kosterlitz–Thouless (BKT) transition in an atomic-scale aluminum nanofilm grown on a GaAs substrate by molecular beam epitaxy (MBE). Such a MBE-grown Al film has a higher superconducting critical temperature and a larger critical magnetic field compared to those of bulk Al. In a 4-nm-thick Al film, our results show that V~I3 can occur in both the low-voltage (the BKT transition temperature TBKT =1.97 K) and high-voltage (TBKT =2.17 K) regions where V and I correspond to the voltage across the device and the driving current, respectively. By fitting our data to the vortex/anti-vortex model and a model based on dynamical scaling, we unequivocally determine that TBKT = 2.17 K in our nanofilm. Our new experimental results suggest that when one uses the temperature for which V~I3 to determine TBKT, great care has to be taken as one also needs to fit one's data to both dynamical scaling and vortex/anti-vortex models. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E08.00012: London penetration depth in Half- Heusler YPdBi and TbPdBi compounds Catalin Martin, Ali S.M. RADMANESH, Yanglin Zhu, Zhiqiang Mao, Leonard Spinu Using the combination of a tunnel diode oscillator (TDO) and a commercial dilution refrigerator, we measured temperature dependent magnetic penetration depth △λ(T) in single crystals of YPdBi and TbPdBi, down to temperatures as low as 0.1K. We found that penetration depths of both compounds do not show exponential temperature dependence and saturation at low temperatures, as expected for conventional BCS superconductors. Instead, in both materials, the penetration depth can be described by a power law △λ(T)=A×Tn . The coeficient A was found to be about 50% smaller in TbPdBi, but the exponents are very similar, n = 2.76 ± 0.04 in YPdBi and n = 2.6 ± 0.3 in TbPdBi, respectively. Our results suggest unconventional superconductivity in both YPdBi and TbPdBi. |
Tuesday, March 5, 2019 10:24AM - 10:36AM |
E08.00013: Effect of magnetic field on short-range antiferromagnetic correlations in the filled skutterudite Pr1-xEuxPt4Ge12 Ram Adhikari, Pengtao Shen, Dom Lal Kunwar, Inho Jeon, M Brian Maple, Maxim Dzero, Carmen Cristina Almasan We have investigated the effects of Eu substitution through thermodynamic measurements on the superconducting filled skutterudite Pr1-xEuxPt4Ge12 in an applied magnetic field H. A heat capacity Schottky anomaly is present over the whole doping range. For the samples with x > 0.5, these peaks shift to lower temperature with increasing applied magnetic field H, hence they reveal the antiferromagnetic (AFM) ordering of the Eu moments, as the AFM transition is suppressed by H. The heat capacity peaks in the samples with x ≤ 0.5 shift to higher temperatures with increasing magnetic field. These latter Schottky peaks are a result of Zeeman splitting by internal magnetic field due to short-range AFM correlations of random magnetic moments of nearing Eu sites, thus increases with Eu concentration x. In low H, the Schottky gaps show a non-linear relationship with H as the magnetic moments become weakly magnetized. In the case of a high applied H, the magnetic moments of Eu sites become completely aligned along H. Thus, Increasing H will not increase further the magnetization, hence the Schottky gaps are a linear function of the external field H. |
Tuesday, March 5, 2019 10:36AM - 10:48AM |
E08.00014: Increase in Birr and reduction of anisotropy of MgB2 with Dy2O3/C co-doping Mike Sumption In this study a series of Dy2O3/C co-doped MgB2 bulks and strands were fabricated. The C – doping level was fixed at 2.0 mol% for all the MgB2 strands. The transport and magnetic properties of MgB2 strands was systematically investigated in terms of Dy2O3 doping level over a wide temperature range. Compared to C-doped-only MgB2 strand, the Dy2O3/C co-doped MgB2 strands have higher transport Jct at 4.2 K. The improved transport Jct – B performance results from the fact that Dy2O3 doping can further improve the anisotropy and flux pinning strength of C-doped MgB2 strand. TEM results of REO doped sample showed nano-size inclusions (20 – 100 nm) present both inside MgB2 grains and on grain boundaries. In-field resistivity measurement (up to 28 T) was performed from 4-40 K. The Bc2 values extracted from both resistivity and magnetic measurements were unchanged by Dy2O3 additives. However, the irreversibility field Bk was increased in response to Dy2O3 doping suggesting a decrease in the anisotropy. The Bk increase, about 1 T between 4-35 K, is of particular interest at higher temperatures (20-30 K). |
Tuesday, March 5, 2019 10:48AM - 11:00AM |
E08.00015: Superconductivity and phase diagram in a transition metal doped Zr5Ge3 compound Xiaoyuan Liu, Sheng Li, Varun Anand, Bing Lv Systematic doping studies have been carried out to search for superconductivity in the transition metal doped Zr5Ge3 system at different sites. Superconductivity is only discovered with Pt doping at Ge site with Tc~2.8K and remain absent with other transition metal doping such as Y, Cr, Ir, and Pd at other different sites. Coincidental with our previous findings in the Zr5Ge3-xRux system, it appears that the induced superconductivity is not only site-selective (only at Ge site) but also dopant selective (only with Pt and Ru dopants). The bulk superconductivity in Zr5Ge3-xPtx has been investigated through resistivity, magnetization, and heat capacity measurements. The superconducting phase diagram of Pt doped Zr5Ge3-xPtx is also proposed. |
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