Hyeonjin Doh

Phenomenological Theory of Superconductivity and Magnetism in Ho 1 − x Dy x Ni 2 B 2 C

The coexistence of the superconductivity and magnetism in the

Specific Heat of Field-dependent Magnetic Orderings in HoNi2B2C

{mathrm{Ho}}_{1ensuremath{-}x}{mathrm{Dy}}_{x}{mathrm{Ni}}_{2}{mathrm{B}}_{2}mathrm{C}

Two-band superconductivity and the effect of pressure in Ho1−xDyxNi2B2C

is studied by using Ginzburg-Laudau theory. This alloy shows the coexistence and complex interplay of superconducting and magnetic order. We propose a phenomenological model which includes two magnetic and two superconducting order parameters accounting for the multiband structure of this material. We describe phenomenologically the magnetic fluctuations and order and demonstrate that they lead to anomalous behavior of the upper critical field. The doping dependence of

UNDULATORY VARIATION OF ANTIFERROMAGNETIC STRENGTH WITH MAGNETIC FIELD BASED ON THE HUBBARD-MODEL HAMILTONIAN

{T}_{c}

Pressure effect on the coexistence of magnetism and superconductivity in Ho1-xDyxNi2B2C

in

A Hubbard model study of antiferromagnetic ground states as a function of external magnetic field

{mathrm{Ho}}_{1ensuremath{-}x}{mathrm{Dy}}_{x}{mathrm{Ni}}_{2}{mathrm{B}}_{2}mathrm{C}

Antiferromagnetic order in doped hubbard model under the magnetic field

showing a reentrance behavior is analyzed yielding very good agreement with experimental data.

The persistent current in frustrated Hubbard model

We have investigated the low-temperature specific heat of HoNi 2 B 2 C down to T = 1 K in various magnetic fields from 0 T to 5 T. At zero field, the specific heat exhibits a large peak at T N = 5.1 K, which is due to commensurate antiferromagnetic ordering, and other smaller peak at T 1 = 5.5 K, which is related to incommensurate ordering. As the field is increased up to 0.5 T, the first peak broadens and moves to a lower temperature, while the other peak at T 1 moves to a higher temperature, which indicates that the phase between T N and T 1 is more favored in magnetic fields. Among possible candidates for the phase, the a -axis modulation phase, which is an extension of a low temperature metamagnetic state, is the most probable. In the high-field region above 1 T, the two-peak feature is replaced by a broad-hill one that fades away with increasing fields, which is the typical smearing feature of the magnetic order at high fields.

Antiferromagnetic phase diagram based on Hubbard model under external magnetic field

Abstract The effect of pressure on the superconductivity and magnetism in Ho1−xDyxNi2B2C is studied both theoretically and experimentally. At P=0 GPa , the breakdown of the de Gennes scaling in this compound for superconducting transition temperatures that are less than the Neel temperature (Tc x=0.1 (T c N ) , increasing pressure decreases Tc, but pressure has no influence on Tc of the x=0.4 sample (Tc>TN). The pressure dependence of the upper critical field also supports the phenomenological theory of multiband superconductivity in an antiferromagnetic state.

Effect of Coulomb repulsion and magnetic frustration on persistent currents in the Hubbard model

Using the Hubbard model Hamiltonian in a mean field level, we examine the variation of antiferromagnetic strength with applied magnetic field. It is demonstrated that minima in the antiferromagnetic strength exist at the the even integer denominator values of rational number for magnetic flux per plaquette. The undulatory behavior of antiferromagnetic strength with the external magnetic field is found. It is seen to be related to the undulatory net statistical phase owing to the influence of the applied magnetic field.