Strong peak in
 T
 c
 of Sr
 2
 RuO
 4
 under uniaxial pressure

Steppke, Alexander; Zhao, Lishan; Barber, Mark E.; Scaffidi, Thomas; Jerzembeck, Fabian; Rösner, H.; Gibbs, Alexandra S.; Maeno, Y.; Simon, Steven H.; Mackenzie, A. P.; Hicks, Clifford W.

doi:10.1126/science.aaf9398

Cited by 267 publications

(285 citation statements)

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“…It should also be mentioned that a superconducting state can exist with an enhanced transition temperature, the so-called 3-K phase. This is observed in eutectic crystals [28][29][30] or in bulk crystals under uniaxial strain [31][32][33].Fluxoid quantization can be investigated by measuring magnetoresistance oscillations as a function of a field applied along the axis of the ring in the regime of the resistive transition, known as the Little-Parks (LP) oscillations [34]. The LP oscillations originate from the oscillations in the free energy and hence in the transition temperature T c , caused by field-induced supercurrents that flow to satisfy the quantization condition.…”

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

et al. 2017

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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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“…1(b). There are indications that the order parameter in the 3-K phase is not ESP [33,35]. However, the LP oscillations are robust, regardless of the pairing symmetry or the number of components of the order parameter.…”

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

et al. 2017

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“…In the case of CaRuO 3 , only recently have films with very low residual resistivities helped to reveal a Fermi liquid ground state below 1.5 K, where previous studies suggested non-Fermi liquid behavior. 7 Moreover, the properties of ruthenates are known to respond dramatically to dimensionality, [8][9][10] strain, [11][12][13] and pressure, 14,15 making them an ideal system for exploring the effects of biaxial strain and dimensional confinement in epitaxial thin films. Therefore, the ability to synthesize ruthenate thin films with extremely low amounts of disorder will be crucial for understanding how their emergent properties and ground states can be manipulated and controlled in thin film form.…”

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Synthesis science of SrRuO3 and CaRuO3 epitaxial films with high residual resistivity ratios

et al. 2018

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Epitaxial SrRuO3 and CaRuO3 films were grown under an excess flux of elemental ruthenium in an adsorption-controlled regime by molecular-beam epitaxy (MBE), where the excess volatile RuOx (x = 2 or 3) desorbs from the growth front leaving behind a single-phase film. By growing in this regime, we were able to achieve SrRuO3 and CaRuO3 films with residual resistivity ratios (ρ300 K/ρ4 K) of 76 and 75, respectively. A combined phase stability diagram based on the thermodynamics of MBE (TOMBE) growth, termed a TOMBE diagram, is employed to provide improved guidance for the growth of complex materials by MBE.

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“…The latter derives from the d xy orbital mainly, with the electronlike Fermi surface slightly below the van Hove points [k = (π/a, 0) and (0, π/a)] with a lattice constant a which we will set equal to 1 in the following. Thus the Fermi surface structure is affected by the physical and/or chemical tunings, such as surface distortion, La doping and strain effects [15][16][17][18][19][20][21][22][23]. These modifications may lead to a Lifshitz transition in the γ band near the van Hove points, which is closely connected with the topological property characterized by the Chern number [24].…”

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Thermal Hall conductivity in the spin-triplet superconductor with broken time-reversal symmetry

2017

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Motivated by the spin-triplet superconductor Sr2RuO4, the thermal Hall conductivity is investigated for several pairing symmetries with broken time-reversal symmetry. In the chiral p-wave phase with a fully opened quasiparticle excitation gap, the temperature dependence of the thermal Hall conductivity has a temperature linear term associated with the topological property directly, and an exponential term, which shows a drastic change around the Lifshitz transition. Examining f -wave states as alternative candidates with d = ∆0ẑ(k 2 x − k 2 y )(kx ± iky) and d = ∆0ẑkxky(kx ± iky) with gapless quasiparticle excitations, we study the temperature dependence of the thermal Hall conductivity, where for the former state the thermal Hall conductivity has a quadratic dependence on temperature, originating from the linear dispersions, in addition to linear and exponential behavior. The obtained result may enable us to distinguish between the chiral p-wave and f -wave states in Sr2RuO4.

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Strong peak in T _c of Sr ₂ RuO ₄ under uniaxial pressure

Cited by 267 publications

References 83 publications

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

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

Synthesis science of SrRuO3 and CaRuO3 epitaxial films with high residual resistivity ratios

Thermal Hall conductivity in the spin-triplet superconductor with broken time-reversal symmetry

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Strong peak in T c of Sr 2 RuO 4 under uniaxial pressure

Cited by 267 publications

References 83 publications

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

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

Synthesis science of SrRuO3 and CaRuO3 epitaxial films with high residual resistivity ratios

Thermal Hall conductivity in the spin-triplet superconductor with broken time-reversal symmetry

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Strong peak in T _c of Sr ₂ RuO ₄ under uniaxial pressure