Low-temperature magnetic penetration depth in d-wave superconductors: Zero-energy bound state and impurity effects

Barash, Yu. S.; Kalenkov, Mikhail S.; Kurkijärvi, J.

doi:10.1103/physrevb.62.6665

Cited by 78 publications

(89 citation statements)

References 46 publications

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“…Also, modulated states in confined geometry are less sensitive to the disorder and would persist much longer in dirty samples compared with surface states. [10] In fact, we find that complete suppression of T * → 0 by impurities happens only when the corresponding suppression of T c is 60% (mean free path ℓ ∼ 5ξ 0 ). It is also reasonable to expect that as long as the OP has significant gradient across the film, the new superconducting phases are only slightly affected by surface roughness.…”

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confidence: 95%

“…3. Previous studies of semi-infinite (1/D → 0) system [10,11,12] show that spontaneous surface current appears already at finite temperature and this indicates that the phase space for q x = 0 state may be enlarged. Also, modulated states in confined geometry are less sensitive to the disorder and would persist much longer in dirty samples compared with surface states.…”

mentioning

confidence: 99%

“…One origin of these states is the interaction of self-induced magnetic field, caused by distortion of the OP, with the OP itself. [8,9,10,11,12] Other current-carrying states arise near surfaces due to subdominant d + is pairing that breaks time-reversal symmetry. [13,14] Finally, new states with triplet structure may appear in quantum wires.…”

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confidence: 99%

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Broken Translational and Time-Reversal Symmetry in Unconventional Superconducting Films

Vorontsov

2009

Phys. Rev. Lett.

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We demonstrate that films of unconventional (d-wave) superconductor at temperatures T 0.43 Tc can exhibit unusual superconducting phases. The new ground states beside the broken gauge and the point group symmetries can spontaneously break (i) continuous translational symmetry and form periodic order parameter structures in the plane of the film, or (ii) time-reversal symmetry and develop supercurrent flowing along the film. These states are result of the strong transverse inhomogeniety present in films with thickness of several coherence lengths. We show a natural similarity between formation of these states and the Fulde-Ferrell-Larkin-Ovchinnikov state.

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confidence: 95%

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Broken Translational and Time-Reversal Symmetry in Unconventional Superconducting Films

Vorontsov

2009

Phys. Rev. Lett.

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“…[17] These states may be shifted away from the Fermi level by a Doppler shift [25]. At temperatures below T (ξ 0 /λ 0 )T c this may occur by spontaneous generation of a finite superfluid momentum, or equivalently, phase gradient in the order parameter [26][27][28]. This effect may then be detected as an anomaly in the low-temperature penetration depth.…”

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confidence: 99%

Spontaneously broken time-reversal symmetry in high-temperature superconductors

Håkansson¹,

Löfwander²,

Fogelström³

2015

Nature Phys

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Conventional superconductors are strong diamagnets that through the Meissner effect expel magnetic fields. It would therefore be surprising if a superconducting ground state would support spontaneous magnetics fields. Such time-reversal symmetry broken states have been proposed for the high-temperature superconductors, but their identification remains experimentally controversial. Here we show a route to a low-temperature superconducting state with broken time-reversal symmetry that may accommodate currently conflicting experiments. This state is characterised by an unusual vortex pattern in the form of a necklace of fractional vortices around the perimeter of the material, where neighbouring vortices have opposite current circulation. This vortex pattern is a result of a spectral rearrangement of current carrying states near the surfaces.The phase-sensitive experiments [1,2] carried out in the early 1990's showed that the high-temperature superconductors have predominantly d-wave pairing symmetry. Ever since, there has been an ongoing debate whether there exists a low-temperature phase that breaks time-reversal (T ) symmetry, in addition to the reflection symmetry of the crystal broken by the d-wave order parameter itself. Several experiments on tunnelling and charge transport support a phase transition into a state with broken T -symmetry at low temperatures [3][4][5][6][7][8]. On the other hand efforts to detect the concomitant spontaneous magnetic field have failed, or at best have put severe restrictions on how strong the subdominant order can be [9][10][11][12][13]. Below we show how to reconcile these two sets of experiments and how the route to a low-temperature superconducting state with broken Tsymmetry may occur. We emphasize that the superconducting state with broken T -symmetry we describe here does not necessarily imply a multicomponent superconducting order-parameter [14,15].The superconducting state in unconventional superconductors, such as the cuprates, is fragile to scattering off impurities, defects and surfaces [16]. Scattering leads to pair-breaking and formation of so-called Andreev states [16][17][18]. These states are formed by constructive normal and Andreev reflection processes, have energies ε A within the superconducting energy gap ∆, and are spatially bound to the scattering centers. For superconducting grains, when the size of the superconducting material is comparable with the superconducting coherence length, the whole superconducting state of the grain is affected by boundary scattering and the formation of Andreev states leads to properties that are not fully understood yet. For the realization of real devices, a deeper understanding of the ground state of grains is therefore called for.We consider meso-scaled grains of a d-wave superconductor and relax the assumption of translational invariance along the surface. The typical grain sizes we consider correspond to side lengths D ∼ 10ξ 0 to 100ξ 0 , where ξ 0 = v F /(2πk B T c ) is the superconducting coherence length (v F is the...

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“…3,5. Stimulated by this theory, extensive studies of MARS in unconventional superconductor junctions have been performed during the last decade: in the case of broken time reversal symmetry state [21][22][23][24][25][26][27][28], in triplet superconductor junctions [29][30][31][32][33][34], in quasi-one-dimensional organic superconductors [35][36][37][38], MARS and Doppler effect [39][40][41][42][43], MARS in ferromagnetic junctions [44][45][46][47][48][49][50][51][52], influence of MARS on Josephson effect [53][54][55][56][57][58][59][60][61][62], and other related problems [63][64][65][66]…”

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confidence: 99%

Impurity scattering effect on charge transport in high-Tc cuprate junctions

Tanaka

Asano

Kashiwaya

2004

Low Temperature Physics

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It is known that the zero-bias conductance peak (ZBCP) is expected in tunneling spectra of normal-metal/high-T c cuprate junctions because of the formation of the midgap Andreev resonant states (MARS) at junction interfaces. In the present review, we report the recent theoretical study of impurity scattering effects on the tunneling spectroscopy. In the former part of the present paper, we discuss impurity effects in normal metal. We calculate tunneling conductance for diffusive normal metal (DN)/high T c cuprate junctions based on the Keldysh Green's function technique. Besides the ZBCP due to the MARS, we can expect ZBCP caused by the different origin, i.e., the coherent Andreev reflection (CAR) assisted by the proximity effect in DN. Their relative importance depends on the angle a between the interface normal and the crystal axis of high-T c superconductors. At a = 0, we find the ZBCP by the CAR for low transparent junctions with small Thouless energies in DN; this is similar to the case of diffusive normal metal/insulator/s-wave superconductor junctions. Under increase of a from zero to p/4, the contribution of MARS to ZBCP becomes more prominent and the effect of the CAR is gradually suppressed. Such complex spectral features would be observable in conductance spectra of high-T c junctions at very low temperatures. In the latter part of our paper, we study impurity effects in superconductors. We consider impurities near the junction interface on the superconductor side. The conductance is calculated from the Andreev and the normal reflection coefficients which are estimated by using the single-site approximation in an analytic calculation and by the recursive Green function method in a numerical simulation. We find splitting of the ZBCP in the presence of the time reversal symmetry. Thus the zero-field splitting of ZBCP in the experiment does not perfectly prove an existence of broken time reversal symmetry state.

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Low-temperature magnetic penetration depth in d-wave superconductors: Zero-energy bound state and impurity effects

Cited by 78 publications

References 46 publications

Broken Translational and Time-Reversal Symmetry in Unconventional Superconducting Films

Broken Translational and Time-Reversal Symmetry in Unconventional Superconducting Films

Spontaneously broken time-reversal symmetry in high-temperature superconductors

Impurity scattering effect on charge transport in high-Tc cuprate junctions

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