Oscillations Of Specific Heat Research Articles

Nodes versus Minima in the Energy Gap of Iron Pnictide Superconductors from Field-Induced Anisotropy

We develop the formalism for computing the oscillations of the specific heat and thermal transport under rotated magnetic field in multiband superconductors with anisotropic gap and apply it to iron-based materials. We show that these oscillations change sign at low temperatures and fields, which strongly influences the experimental conclusions about the gap structure. We find that recent measurements of the specific heat oscillations indicate that the iron-based superconductors possess an anisotropic gap with deep minima or nodes close to the line connecting electron and hole pockets. We predict the behavior of the thermal conductivity that will help distinguish between these cases.

Fractality of Hofstadter Butterfly in Specific Heat Oscillation

We calculate thermodynamical properties of the Hofstadter model using a recently developed quantum transfer matrix method. We find intrinsic oscillation features in specific heat that manifest the fractal structure of the Hofstadter butterfly. We also propose experimental approaches which use specific heat as an access to detect the Hofstadter butterfly.

Vortex State and Field-Angle Resolved Specific Heat Oscillation forH∥abind-Wave Superconductors

When magnetic field is applied parallel to the ab plane in d_{x^2-y^2}-wave superconductors, the transition of stable vortex lattice structure, spatial structure of local density of states, and specific heat oscillation by rotation of magnetic field orientation are investigated by quantitative calculations based on the selfconsistent Eilenberger theory. We estimate how the vortex state changes depending on the relative angle between the node-direction of the superconducting gap and magnetic field orientation. To reproduce the sign-change of specific heat oscillation observed in CeCoIn_5, our study is done by including strong paramagnetic effect. The quantitative theoretical calculations give decisive information to analyze the experimental data on the field-angle dependence, and establish the angle-resolved specific heat experiment as a spectroscopic means to identify the node-position of the superconducting gap.

Location of gap nodes in the organic superconductorsκ−(ET)2Cu(NCS)2andκ−(ET)2Cu[N(CN)2]Brdetermined by magnetocalorimetry

We report specific heat measurements of the organic superconductors $\kappa$-(ET)$_2$Cu(NCS)$_2$ and $\kappa$-(ET)$_2$Cu[N(CN)$_2$]Br. When the magnetic field is rotated in the highly conducting planes at low temperature ($T\simeq 0.4$ K), we observe clear oscillations of specific heat which have a strong fourfold component. The observed strong field and temperature dependence of this fourfold component identifies it as originating from nodes in the superconducting energy gap which point along the in-plane crystal axes ($d_{xy}$ symmetry)

Inversion of specific heat oscillations with in-plane magnetic field angle in two-dimensionald-wave superconductors

Experiments on several novel superconducting compounds have observed oscillations of the specific heat when an applied magnetic field is rotated with respect to the crystal axes. The results are commonly interpreted as arising from the nodes of an unconventional order parameter, but the identifications of nodal directions are sometimes controversial. Here we show with a semiclassical model calculation that when the magnetic field points in the direction of the nodes, either minima or maxima can occur in the specific heat depending on the temperature $T$ and the magnetic field $H$. An inversion of the angular oscillations takes place with respect to those predicted earlier at low temperature by the nodal approximation. This result, together with the argument that the inversion takes place based on an approximation valid at moderate fields, indicates that the inversion of specific heat oscillations is an intrinsic feature of nodal superconductors.

Theory of gap-node detection by angle-resolved specific heat measurement

The specific heat oscillation in the mixed state of type II superconductors is studiedtheoretically when rotating a field within a plane containing a gap minimum andmaximum. The calculations are performed microscopically by solving the quasi-classicalEilenberger equation for vortex lattices. The field dependence of the oscillation amplitudecan discriminate between the nodal and anisotropic gap with a finite minimum and theoscillation phase gives the gap minimum position on the Fermi surface. These alsoprovide a way to separate out the anisotropic behaviour due to the Fermi velocity.

Specific heat properties of electrons in generalized Fibonacci quasicrystals

The purpose of this paper is to investigate the specific heat properties of electrons in one-dimensional quasiperiodic potentials, arranged in accordance with the generalized Fibonacci sequence. The electronic energy spectra are calculated using the one-dimensional Schrödinger equation in a tight-binding approximation. Both analytical and numerical results on the temperature dependence of the electron's specific heat associated with their multiscale fractal energy spectra are presented. We compare our numerical results with those found for the ordinary Fibonacci structure. A rich and varied behavior is found for the specific heat oscillations when T→0, with interesting physical consequences.

Specific heat oscillations in quasi-periodic structures

Most models on quasi-crystals, as well as the related experimental results, exhibit fractal energy spectra. We discuss the relevant thermodynamic implications of this feature by performing both analytical and numerical calculations of the specific heats associated with successive hierarchical approximations to fractal energy spectra. Instructive anomalies are displayed, namely the specific heat exhibits an infinite number of small-amplitude oscillations symmetrically disposed around a characteristic dimension of the spectrum. We also analyse a multifractal spectrum generated dynamically by the logistic map and conjecture a possible connection with Tsallis' generalized thermostatics.

New type of magnetic resonance and giant quasi-one-dimensional fluctuations in organic superconductors

We consider the fluctuation contribution to free energy of a quasi-one-dimensional (Q1D) metal due to electron-electron (“eee”) interaction in magnetic field. Electron paramagnetic momentum is found to become strongly temperature and pressure dependent in a boad temperature region, T ⪅ 200K. Electron specific heat also has large fluctuation correction and exhibit nontrivial temperature behaviour. As a result of the influence of Zeeman-splitting on processes of “e-e”-scattering, new angular oscillations of specific heat occur in magnetic field.

Magneto-quantum oscillations of the specific heat in the Bechgaard salt (TMTSF)2ClO4

We have performed measurements of the magnetic field dependence of the low temperature specific heat at a series of fixed temperatures up to 30 tesla. In addition to the direct thermodynamic observation of a second order phase transition from the magnetic field induced spin density wave (SDW) state to the re-entrant metallic state, we also observed large quantum oscillations periodic in inverse magnetic field with a temperature independent frequency of 257 tesla. Both the size of the specific heat oscillations and their apparent continuation into the high field metallic state call into question current models for their physical origin.