Unconventional quantum oscillations in mesoscopic rings of spin-triplet superconductor Sr<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub></mml:math>RuO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>4</mml:mn></mml:msub></mml:math>

In a microring of a superconductor with a spin-triplet equal-spin pairing state, a fluxoid, a combined object of magnetic flux and circulating supercurrent, can penetrate as half-integer multiples of the flux quantum. A candidate material to investigate such half-quantum fluxoids is Sr 2 RuO 4 . We fabricated Sr 2 RuO 4 microrings using single crystals and measured their resistance behavior under magnetic fields controlled with a three-axis vector magnet. Proper Little-Parks oscillations in the magnetovoltage as a function of an axially applied field, associated with fluxoid quantization, are clearly observed using bulk single-crystalline superconductors. We then performed magnetovoltage measurements with additional in-plane magnetic fields. By carefully analyzing both the voltages V + (V − ) measured at positive (negative) current, we find that, above an in-plane threshold field of about 10 mT, the magnetovoltage maxima convert to minima. We interpret this behavior as the peak splitting expected for the half-quantum fluxoid states. DOI: 10.1103/PhysRevB.96.180507 Recently, it has been recognized that Majorana particles, which have unusual equivalence to their own antiparticles and have been long sought in elementary particle physics, can be realized as quasiparticle excitation in condensed-matter systems such as topological superconductors [1]. In particular, Majorana zero modes (MZMs), the zero-energy states of the Majorana branch, have attracted much attention since MZMs do not obey ordinary Abelian statistics and can be utilized for quantum computing [2,3]. Thus, direct detection of MZMs has become a holy grail of current condensed-matter physics [4,5]. Half-quantum fluxoid (HQF) [6] in a spin-triplet superconductor or a superfluid is known to host such MZMs [7,8].An additional phase degree of freedom in a superconducting wave function is the key ingredient for the realization of HQF states. For a spin-singlet superconducting ring with wave function ψ S = | S |e iθ , the single-valuedness of ψ S requires quantization = n 0 [integer-quantum fluxoid (IQF)] inside a closed path. Here, n is an integer, is the fluxoid, and 0 = h/2e is the flux quantum with h the Planck constant and e the elementary charge. Note that, in a superconductor smaller than the penetration depth, the fluxoid, which contains an integration of the supercurrent along a closed path, is quantized, rather than the flux. For a spin-triplet equal-spin pairing (ESP) superconductor, the wave function ψ T = | T |(−e iθ ↑ |↑↑ + e iθ ↓ |↓↓ ) has two phase degrees of freedom. In an ESP ring, half-integer quantization = n 0 with n = ±1/2, ± 3/2, . . . is allowed even under the constraint of the single-valuedness of the wave function. Such a fluxoid state is called the HQF state.One of the materials that can host the HQF is Sr 2 RuO 4 , which is a leading candidate spin-triplet ESP superconductor [9,10]. This oxide has a layered perovskite structure and exhibits superconductivity below 1.5 K. Various experiments have provided firm evidence for the sp...

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“…In-plane magnetic field [38,39]. However, the oscillation amplitudes were substantially larger than the LP expectation.…”

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confidence: 85%

Little-Parks oscillations with half-quantum fluxoid features in Sr2RuO4 microrings

et al. 2017

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“…Static few vortex states in mesoscopic superconductors have been studied previously both theoretically [12][13][14][15][16] and experimentally [17][18][19][20][21][22][23][24][25], with an impressive accumulation of detailed understanding. Studies of vortex motion have also been carried out [26][27][28][29][30] and have led to interesting findings such as vortex-crossing-induced magnetoresistance oscillations [27,29,30] with an amplitude much larger than that of the traditional Little-Parks effect [31]. Nevertheless, the manipulation of the vortex motion in these mesoscopic devices has yet to be pursued systematically.…”

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confidence: 99%

Vortex crossing and trapping in doubly connected mesoscopic loops of a single-crystal type-II superconductor

Mills

Shen

et al. 2015

Phys. Rev. B

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Numerical calculations on a mesoscopic ring of a type II superconductor in the London limit suggest that an Abrikosov vortex can be trapped in such a structure above a critical magnetic field and generate a phase shift in the magnetoresistance oscillations. We prepared submicron-sized superconducting loops of single-crystal, type II superconductor NbSe2 and measured magnetoresistance oscillations resulting from vortices crossing the loops. The free energy barrier for vortex crossing determines the crossing rate and is periodically modulated by the external magnetic flux threading the loop. We demonstrated experimentally that the crossing of vortices can be directed at a pair of constrictions in the loop, leading to more pronounced magnetoresistance oscillations than those in a uniform ring. The vortex trapping in both a simple ring and a ring featuring two constrictions was found to result in a phase shift in the magnetoresistance oscillations as predicted in the numerical calculations. The controlled crossing and trapping of vortices demonstrated in our NbSe2 devices provide a starting point for the manipulation of individual Abrikosov vortices, which is useful for future technologies.

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“…These half-height steps are consistent with the existence of a half-flux-quantum (Φ 0 /2 = h/4e) state in Sr 2 RuO 4 . Little-Parks resistance oscillation measurements on superconducting mesoscopic rings of Sr 2 RuO 4 have been carried out 108 in order to obtain additional, independent evidence for the existence of half-fluxquantum state in Sr 2 RuO 4 . Because superconducting films of Sr 2 RuO 4 are not yet available, develop a technique to prepare mesoscopic rings of Sr 2 RuO 4 using thin, flat crystals that are in turn prepared by mechanical exfoliation from bulk single crystals.…”

Section: Mesoscopic Size Sr 2 Ruo 4 and The Existence Of Half-flux-qumentioning

confidence: 99%

Unconventional superconductivity in Sr2RuO4

Liu

Mao

2015

Physica C: Superconductivity and its Applications

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Please cite this article as: Y. Liu, Z-Q. Mao, Unconventional superconductivity in Sr 2 RuO 4 , Physica C (2015), doi: http://dx. AbstractSr 2 RuO 4 , featuring a layered perovskite crystalline and quasi-two-dimensional electronic structure, was first synthesized in 1957. Unconventional, p-wave pairing was predicted for Sr 2 RuO 4 by Rice and Sigrist and Baskaran shortly after superconductivity in this material was discovered in 1994. Experimental evidence for unconventional superconductivity in Sr 2 RuO 4 has obtained in the past two decades and reviewed previously. In this article, we will first discuss constraints on the pairing symmetry and the mechanism of superconductivity in Sr 2 RuO 4 and summarise experimental evidence supporting the unconventional pairing symmetry accumulated to date. We will then present several aspects of the experimental determination of the unconventional superconductivity in Sr 2 RuO 4 in some detail. In particular, we will discuss the phase-senistive measurements that have played an important role in the determination of the pairing symmetry in Sr 2 RuO 4 . The responses of superconductivity to the mechanical perturbations and their implications on the mechanism of superconductivity are discussed. A brief survey of various non-bulk Sr 2 RuO 4 is also included to illustrate the many unusual features resulted from the unconventional nature of superconductivity in this material system. Finally, we will discuss some outstanding unresolved issues on Sr 2 RuO 4 and provide an outlook of the future work on Sr 2 RuO 4 .

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Unconventional quantum oscillations in mesoscopic rings of spin-triplet superconductor Sr2RuO4

Cited by 37 publications

References 22 publications

Little-Parks oscillations with half-quantum fluxoid features in Sr2RuO4 microrings

Little-Parks oscillations with half-quantum fluxoid features in Sr2RuO4 microrings

Vortex crossing and trapping in doubly connected mesoscopic loops of a single-crystal type-II superconductor

Unconventional superconductivity in Sr2RuO4

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