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P. Miranovic

Publications and source records attributed to P. Miranovic.

11 recordsLinked to original sources
arXiv2007

Field-angle-dependent specific heat measurements and gap determination of a heavy fermion superconductor URu2Si2

To identify the superconducting gap structure in URu2Si2 we perform field-angle-dependent specific heat measurements for the two principal orientations in addition to field rotations, and theoretical analysis based on microscopic calculations. The Sommerfeld coefficient γ(H)'s in the mixed state exhibit distinctively different field-dependence. This comes from point nodes and substantial Pauli paramagnetic effect of URu2Si2. These two features combined give rise to a consistent picture of superconducting properties, including a possible first order transition of Hc2 at low temperatures.

cond-mat.str-el↗
arXiv2006

Ubiquitous V-shape density of states in mixed state of clean limit type II superconductors; STM experiment and theory

It is demonstrated theoretically and experimentally that the low energy density of states $N(E)$ is described by a singular V-shape form $N(E)=N_0(H)+α|E|+O(E^2)$ for all clean superconductors in a vortex state, irrespective of the underlying gap structure. The linear term $α|E|$ which has been not recognized so far is obtained by exactly evaluating the vortex contribution. Based on microscopic Eilenberger theory $N(E)$ is evaluated for isotropic gap, line and point node gaps to yield a V-shape $N(E)$. STS-STM experiments on NbSe$_2$ and YNi$_2$B$_2$C give direct evidence for this. We provide arguments on significance of this finding and on relevance to other experiments.

cond-mat.supr-con↗
arXiv2006

Specific heat and low-lying excitations in the mixed state for a type II superconductor

Low temperature behavior of the electronic specific heat $C(T)$ in the mixed state is by the self-consistent calculation of the Eilenberger theory. In addition to $γT$-term ($γ$ is a Sommerfeld coefficient), $C(T)$ has significant contribution of $T^2$-term intrinsic in the vortex state. We identify the origin of the $T^2$-term as (i) V-shape density of states in the vortex state and (ii) Kramer-Pesch effect of vortex core shrinking upon lowering $T$. These results both for full-gap and line node cases reveal that the vortex core is a richer electronic structure beyond the normal core picture.

cond-mat.supr-con↗
arXiv2004

How to detect gap nodes of a superconductor by angle-resolved specific heat experiment?

The specific heat oscillation in the mixed state of type II superconductors is studied theoretically when rotating field within a plane containing gap minimum and maximum. The calculations are performed microscopically by solving quasi-classical Eilenberger equation for vortex lattices. The field dependence of the oscillation amplitude can discriminate between the nodal and anisotropic gap with a finite minimum and the oscillation phase gives the gap minimum position on the Fermi surface. These also provide a way to separate out the anisotropic behavior due to the Fermi velocity.

cond-mat.supr-con↗
arXiv2003

The effect of nonmagnetic impurities on the local density of states in s-wave superconductors

We study the effect of nonmagnetic impurities on the local density of states (LDOS) in s-wave superconductors. The quasiclassical equations of superconductivity are solved selfconsistently to show how LDOS evolves with impurity concentration. The spatially averaged zero-energy LDOS is a linear function of magnetic induction in low fields, N(E=0)=cB/H_{c2}, for all impurity concentration. The constant of proportionality "c" depends weakly on the electron mean free path. We present numerical data for differential conductance and spatial profile of zero-energy LDOS which can help in estimating the mean free path through the LDOS measurement.

cond-mat.supr-con↗
arXiv2003

Field-angle Dependence of the Zero-Energy Density of States in the Unconventional Heavy-Fermion Superconductor CeCoIn5

Field-angle dependent specific heat measurement has been done on the heavy-fermion superconductor CeCoIn5 down to ~ 0.29 K, in a magnetic field rotating in the tetragonal c-plane. A clear fourfold angular oscillation is observed in the specific heat with the minima (maxima) occurring along the [100] ([110]) directions. Oscillation persists down to low fields H << Hc2, thus directly proving the existence of gap nodes. The results indicate that the superconducting gap symmetry is most probably of dxy type.

cond-mat.str-el↗
arXiv2003

Orientational field-dependence of low-lying excitations in mixed state of unconventional superconductors

Orientational field-dependence of the zero energy density of states (ZEDOS) is calculated for superconductors with the polar state (line node), axial state (point node) and 3D d-wave state. Depending on the gap topology and relative field direction the field dependencies of ZEDOS sensitively differ, providing us a useful and practical method to identify the gap topology. It is also demonstrated that for d-wave state the field rotation in the basal plane shows a sizable oscillation ~3% of ZEDOS. This is directly measurable in low-T specific heat experiment in the mixed state.

cond-mat.supr-con↗
arXiv2002

Anisotropy of the superconducting state properties and phase diagram of MgB2 by torque magnetometry on single crystals

The angular and temperature dependence of the upper critical field Hc2 in MgB2 was determined from torque magnetometry measurements on single crystals. The Hc2 anisotropy gamma_H was found to decrease with increasing temperature, in disagreement with the anisotropic Ginzburg-Landau theory, which predicts that the gamma_H is temperature independent. This behaviour can be explained by the two band nature of superconductivity in MgB2. An analysis of measurements of the reversible torque in the mixed state yields a field dependent effective anisotropy gamma_eff, which can be at least partially explained by different anisotropies of the penetration depth and the upper critical field. It is shown that a peak effect in fields of about 0.85 Hc2 is a manifestation of an order-disorder phase transition of vortex matter. The H-T phase diagram of MgB2 for H//c correlates with the intermediate strength of thermal fluctuations in MgB2, as compared to those in high and low Tc superconductors.

cond-mat.supr-con↗
arXiv2002

Thermodynamics and magnetic field profiles in low-kappa type-II superconductors

Two-dimensional low-kappa type-II superconductors are studied numerically within the Eilenberger equations of superconductivity. Depending on the Ginzburg-Landau parameter κ=λ/ξvortex-vortex interaction can be attractive or purely repulsive. The sign of interaction is manifested as a first (second) order phase transition from Meissner to the mixed state. Temperature and field dependence of the magnetic field distribution in low-kappa type-II superconductors with attractive intervortex interaction is calculated. Theoretical results are compared to the experiment.

cond-mat.supr-con↗
arXiv2001

Elastic moduli of vortex lattices within nonlocal London model

Vortex lattice (VL) elastic response is analyzed within nonlocal London model. The squash modulus turns zero at the field $H_{\Box}$ where VL undergoes square-to-rhombus structural transition. In the field region $H>H_{\Box}$ where the square VL is stable, the rotation modulus turns zero at a field $H_r$ indicating instability of the square VL with respect to rotations. The shear modulus depends on the shear direction; the dependence is strong in the vicinity of $H_{\Box}$ where the square VL is soft with respect to the shear along [110]. The $H$ dependences of elastic moduli are evaluated for LuNi$_2$B$_2$C.

cond-mat.supr-con↗