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J. E. Sonier

Publications and source records attributed to J. E. Sonier.

At least 55 records · Page 3Linked to original sources
arXiv2008

Inhomogeneous Magnetic-Field Response of YBa2Cu3Oy and La2-xSrxCuO4 Persisting above the Bulk Superconducting Transition Temperature

We report that in YBa2Cu3Oy and La2-xSrxCuO4 there is a spatially inhomogeneous response to magnetic field for temperatures T extending well above the bulk superconducting transition temperature Tc. An inhomogeneous magnetic response is observed above Tc even in ortho-II YBa2Cu3O6.50, which has highly ordered doping. The degree of the field inhomogeneity above Tc tracks the hole doping dependences of both Tc and the density of the superconducting carriers below Tc, and therefore is apparently coupled to superconductivity.

cond-mat.supr-con↗
arXiv2008

Comment on "Magnetic Order in the Pseudogap Phase of High-Tc Superconductors''

In a recent Letter, Fauque et al. [Phys. Rev. Lett. 96, 197001 (2006)] reported the detection of a novel magnetic order in YBCO near the pseudogap transition temperature T*. They remark that this magnetic order has not been clearly identified by local probes and, in particular, by muon spin resonance. The purpose of this Comment is to point out that this is untrue, and together with the more recent detection of broken time reversal symmetry by polar Kerr effect measurements [J. Xia et al. Phys. Rev. Lett. 100, 127002 (2008)], there are now three very different kinds of experiments that provide evidence for this magnetic transition.

cond-mat.supr-con↗
arXiv2008

Muon spin rotation studies of electronic excitations and magnetism in the vortex cores of superconductors

The focus of this paper is on recent progress in muon spin rotation (muSR) studies of the vortex cores in type-II superconductors. By comparison of muSR measurements of the vortex core size in a variety of materials with results from techniques that directly probe electronic states, the effect of delocalized quasiparticles on the spatial variation of field in a lattice of interacting vortices has been determined for both single-band and multi-band superconductors. These studies demonstrate the remarkable accuracy of what some still consider an exotic technique. In recent years muSR has also been used to search for magnetism in and around the vortex cores of high-temperature superconductors. As a local probe muSR is specially suited for detecting static or quasistatic magnetism having short-range or random spatial correlations. As discussed in this review, muSR experiments support a generic phase diagram of competing superconducting and magnetic order parameters, characterized by a quantum phase transition to a state where the competing order is spatially nonuniform.

cond-mat.supr-con↗
arXiv2007

Role of CuO chains in vortex core structure in YBa2Cu3O{7-delta}

The Bogoliubov-deGennes equations are solved for a proximity model for YBa_2Cu_3O_{7-δ} in a magnetic field. The model explicitly includes the effects of the one-dimensional CuO chains, whose influence on the vortex core structure is studied. The rapid vortex core contraction as a function of field which is seen experimentally at low magnetic fields is naturally explained by the presence of the chains.

cond-mat.supr-con↗
arXiv2007

Spin-glass state of vortices in YBa2Cu3Oy and La2-xSrxCuO4 below the metal-to-insulator crossover

Highly disordered magnetism confined to individual weakly interacting vortices is detected by muon spin rotation in two different families of high-transition-temperature superconductors, but only in samples on the low-doping side of the low-temperature normal state metal-to-insulator crossover (MIC). The results support an extended quantum phase transition (QPT) theory of competing magnetic and superconducting orders that incorporates the coupling between CuO2 planes. Contrary to what has been inferred from previous experiments, the static magnetism that coexists with superconductivity near the field-induced QPT is not ordered. Our findings unravel the mystery of the MIC and establish that the normal state of high-temperature superconductors is ubiquitously governed by a magnetic quantum critical point in the superconducting phase.

cond-mat.supr-con↗
arXiv2007

Hole doping dependences of the magnetic penetration depth and vortex core size in YBa2Cu3Oy: Evidence for stripe correlations near 1/8 hole doping

We report on muon spin rotation measurements of the internal magnetic field distribution n(B) in the vortex solid phase of YBa2Cu3Oy (YBCO) single crystals, from which we have simultaneously determined the hole doping dependences of the in-plane Ginzburg-Landau (GL) length scales in the underdoped regime. We find that Tc has a sublinear dependence on 1/lambda_{ab}^2, where lambda_{ab} is the in-plane magnetic penetration depth in the extrapolated limits T -> 0 and H -> 0. The power coefficient of the sublinear dependence is close to that determined in severely underdoped YBCO thin films, indicating that the same relationship between Tc and the superfluid density is maintained throughout the underdoped regime. The in-plane GL coherence length (vortex core size) is found to increase with decreasing hole doping concentration, and exhibit a field dependence that is explained by proximity-induced superconductivity on the CuO chains. Both the magnetic penetration depth and the vortex core size are enhanced near 1/8 hole doping, supporting the belief by some that stripe correlations are a universal property of high-Tc cuprates.

cond-mat.supr-con↗
arXiv2007

Multiband superconductivity and penetration depth in PrOs4Sb12

The effective superconducting penetration depth measured in the vortex state of PrOs4Sb12 using transverse-field muon spin rotation (TF-muSR) exhibits an activated temperature dependence at low temperatures, consistent with a nonzero gap for quasiparticle excitations. In contrast, Meissner-state radiofrequency (rf) inductive measurements of the penetration depth yield a T^2 temperature dependence, suggestive of point nodes in the gap. A scenario based on the recent discovery of extreme two-band superconductivity in PrOs4Sb12 is proposed to resolve this difference. In this picture a large difference between large- and small-gap coherence lengths renders the field distribution in the vortex state controlled mainly by supercurrents from a fully-gapped large-gap band. In zero field all bands contribute, yielding a stronger temperature dependence to the rf inductive measurements.

cond-mat.supr-con↗
arXiv2006

Avoided Quantum Criticality in YBa_2Cu_3O_y and La_{2-x}Sr_xCuO_4

Spin-glass magnetism confined to individual weakly interacting vortices is detected in two different families of high-transition-temperature (T_c) superconductors, but only in samples on the low-doping side of the low-temperature normal state metal-to-insulator crossover (MIC). Our findings unravel the mystery of the MIC, but more importantly identify the true location of the field-induced quantum phase transition (QPT) in the superconducting state. The non-uniform appearance of magnetism in the vortex state favours a surprisingly exotic phase diagram, in which spatially inhomogeneous competing order is stabilized at the QPT, and an `avoided' quantum critical point (QCP) is realized at zero magnetic field.

cond-mat.supr-con↗
arXiv2006

Muon spin rotation measurements of the vortex state in vanadium: A comparative analysis using iterative and analytical solutions of the Ginzburg-Landau equations

We report muon spin rotation measurements on a single crystal of the marginal type-II superconductor V. The measured internal magnetic field distributions are modeled assuming solutions of the Ginzburg-Landau (GL) equations for an ideal vortex lattice obtained using (i) an iterative procedure developed by E.H. Brandt, Phys. Rev. Lett. 78, 2208 (1997) and (ii) a variational method. Both models yield qualitatively similar results. The magnetic penetration depth (lambda) and the GL coherence length (xi) determined from the data analysis exhibit strong field dependences, which are attributed to changes in the electronic structure of the vortex lattice. The zero-field extrapolated values of lambda and the GL parameter kappa agree well with values obtained by other experimental techniques that probe the Meissner state.

cond-mat.supr-con↗
arXiv2006

Effect of Delocalized Vortex Core States on the Specific Heat of Nb

The magnetic field (B) dependence of the electronic specific heat for a simple BCS type-II superconductor has been determined from measurements on pure niobium (Nb). Contrary to expectations, the electronic specific heat coefficient gamma(T,B) is observed to be a sublinear function of B at fields above the lower critical field H_{c1}. This behavior is attributed to the delocalization of quasiparticles bound to the vortex cores. The results underscore the ambiguity of interpretation that arises in specific heat studies of this kind on newly discovered type-II superconductors, and also emphasize the need to such measurements under field-cooled conditions.

cond-mat.supr-con↗
arXiv2005

Field dependence of the vortex core size in a multi-band superconductor

The magnetic field dependence of the vortex core size in the multi-band superconductor NbSe2 has been determined from muon spin rotation measurements. The spatially extended nature of the quasiparticle core states associated with the smaller gap leads to a rapid field-induced shrinkage of the core size at low fields, while the more tightly bound nature of the states associated with the larger gap leads to a field-independent core size for fields greater than 4 kOe. A simple model is proposed for the density of delocalized core states that establishes a direct relationship between the field-induced reduction of the vortex core size and the corresponding enhancement of the electronic thermal conductivity. We show that this model accurately describes both NbSe2 and the single-band superconductor V3Si.

cond-mat.supr-con↗
arXiv2005

Penetration depth, symmetry breaking, and gap nodes in superconducting PrOs4Sb12

Transverse-field muon spin relaxation rates in single crystals of the heavy-fermion superconductor PrOs4Sb12 (Tc = 1.85 K) are nearly constant in the vortex state for temperatures below ~0.5Tc. This suggests that the superconducting penetration depth lambda(T) is temperature-independent at low temperatures, consistent with a gapped quasiparticle excitation spectrum. In contrast, radiofrequency measurements yield a stronger temperature dependence of lambda(T), indicative of point nodes in the gap. A similar discrepancy exists in superconducting Sr2RuO4 which, like PrOs4Sb12, breaks time-reversal symmetry (TRS) below Tc, but not in a number of non-TRS-breaking superconductors.

cond-mat.supr-con↗
arXiv2004

Investigations of the Core Structure of Magnetic Vortices in Type-II Superconductors by muSR

Muon spin rotation (muSR) has emerged as the leading experimental probe of the effective size of magnetic vortices in type-II superconductors. muSR data on several different classes of type-II superconductors shows that the inner structure of a vortex can depend quite strongly on temperature and the strength of the external magnetic field. In this paper it is shown that these behaviours are related to the quasiparticle excitation spectrum both inside and outside of the vortex cores. Here we establish that the vortex-core size determined by muSR is particularly sensitive to the nature of the superconducting energy gap(s) and the symmetry of the Fermi surface. A survey of results for different superconductors arrives at the conclusion that the large vortex-core size observed by muSR in YBa2Cu3O6.95 is due to CuO chain superconductivity.

cond-mat.supr-con↗
arXiv2004

Disorder, inhomogeneity and spin dynamics in f-electron non-Fermi liquid systems

Muon spin rotation and relaxation ($μ$SR) experiments have yielded evidence that structural disorder is an important factor in many f-electron-based non-Fermi-liquid (NFL) systems. Disorder-driven mechanisms for NFL behaviour are suggested by the observed broad and strongly temperature-dependent $μ$SR (and NMR) linewidths in several NFL compounds and alloys. Local disorder-driven theories (Kondo disorder, Griffiths-McCoy singularity) are, however, not capable of describing the time-field scaling seen in muon spin relaxation experiments, which suggest cooperative and critical spin fluctuations rather than a distribution of local fluctuation rates. A strong empirical correlation is established between electronic disorder and slow spin fluctuations in NFL materials

cond-mat.str-el↗
arXiv2004

Shrinking Magnetic Vortices in V3Si Due to Delocalized Quasiparticle Core States: Confirmation of the Microscopic Theory for Interacting Vortices

We report muon spin rotation measurements on the conventional type-II superconductor V3Si that provide clear evidence for changes to the inner structure of a vortex due to the delocalization of bound quasiparticle core states. The experimental findings described here confirm a key prediction of recent microscopic theories describing interacting vortices. The effects of vortex-vortex interactions on the magnetic and electronic structure of the vortex state are of crucial importance to the interpretation of experiments on both conventional and exotic superconductors in an applied magnetic field.

cond-mat.supr-con↗
arXiv2003

Superconductivity and Field-Induced Magnetism in Pr$_{2-x}$Ce$_x$CuO$_4$ Single Crystals

We report muon-spin rotation/relaxation (muSR) measurements on single crystals of the electron-doped high-T_c superconductor Pr$_{2-x}$Ce$_x$CuO$_4$. In zero external magnetic field, superconductivity is found to coexist with Cu spins that are static on the muSR time scale. In an applied field, we observe a Knight shift that is primarily due to the magnetic moment induced on the Pr ions. Below the superconducting transition temperature T_c, an additional source of static magnetic order appears throughout the sample. This finding is consistent with antiferromagnetic ordering of the Cu spins in the presence of vortices. We also find that the temperature dependence of the in-plane magnetic penetration depth in the vortex state resembles that of the hole-doped cuprates at temperatures above ~ 0.2 T_c.

cond-mat.supr-con↗
arXiv2003

Local Magnetic Susceptibility of the Positive Muon in the Quasi 1D S=1/2 Antiferromagnet dichlorobis (pyridine) copper (II)

We report muon spin rotation measurements of the local magnetic susceptibility around a positive muon in the paramagnetic state of the quasi one-dimensional spin 1/2 antiferromagnet dichlorobis (pyridine) copper (II). Signals from three distinct sites are resolved and have a temperature dependent frequency shift which is significantly different than the magnetic susceptibility. This difference is attributed to a muon induced perturbation of the spin 1/2 chain. The obtained frequency shifts are compared with Transfer Matrix DMRG numerical simulations.

cond-mat.str-el↗