Proximity to a critical point driven by electronic entropy in URu2Si2

AbstractThe strongly correlated actinide metal URu2Si2 exhibits a mean field-like second order phase transition at To ≈ 17 K, yet lacks definitive signatures of a broken symmetry. Meanwhile, various experiments have also shown the electronic energy gap to closely resemble that resulting from hybridization between conduction electron and 5f-electron states. We argue here, using thermodynamic measurements, that the above seemingly incompatible observations can be jointly understood by way of proximity to an entropy-driven critical point, in which the latent heat of a valence-type electronic instability is quenched by thermal excitations across a gap, driving the transition second order. Salient features of such a transition include a robust gap spanning highly degenerate features in the electronic density of states, that is weakly (if at all) suppressed by temperature on approaching To, and an elliptical phase boundary in magnetic field and temperature that is Pauli paramagnetically limited at its critical magnetic field.

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Electronic Energy Gap in Ferromagnets Due to a Strong Internal Magnetic Field

Physical Review B ◽

10.1103/physrevb.4.1602 ◽

1971 ◽

Vol 4 (5) ◽

pp. 1602-1603 ◽

Cited By ~ 1

Author(s):

Robert W. Danz

Keyword(s):

Magnetic Field ◽

Energy Gap ◽

Electronic Energy ◽

Internal Magnetic Field

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Critical Magnetic Field and Energy-Gap Anisotropy of Zinc

Physical Review B ◽

10.1103/physrevb.7.4118 ◽

1973 ◽

Vol 7 (9) ◽

pp. 4118-4123 ◽

Cited By ~ 8

Author(s):

D. U. Gubser ◽

J. E. Cox

Keyword(s):

Magnetic Field ◽

Energy Gap ◽

Critical Magnetic Field ◽

Gap Anisotropy

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Magnetoresistance of TTF-TCNQ

Canadian Journal of Physics ◽

10.1139/p75-202 ◽

1975 ◽

Vol 53 (17) ◽

pp. 1593-1605 ◽

Cited By ~ 46

Author(s):

T. Tiedje ◽

J. F. Carolan ◽

A. J. Berlinsky ◽

L. Weiler

Keyword(s):

Magnetic Field ◽

Applied Field ◽

Energy Gap ◽

Electronic Energy ◽

Insulator Transition ◽

Metal Insulator Transition ◽

Metal Insulator ◽

Peierls Transition ◽

Scattering Time ◽

The Magnetic Field

The magnetoresistance of TTF-TCNQ has been measured for currents along the crystallographic b axis in static fields of 50 kOe for temperatures between 17 and 98 K. For [Formula: see text] the magnetoresistance Δρ/ρ = [ρ(50 kOe) − ρ(0)]/ρ(0) is less than 0.1% in magnitude. There is a peak of about −1.4% at 52.8 ± 0.2 K. Below 50 K, Δρ/ρ is small and negative and is described reasonably well by the formula Δρ/ρ = −(1/2)(μBH/kT)2. At all temperatures Δρ/ρ was found to be approximately independent of the orientation of the applied field with respect to the current. The high temperature behavior is consistent with that expected for a metal in the short scattering time limit [Formula: see text]. We attribute the peak at 52.8 K to the suppression of the metal–insulator transition by the magnetic field, and we show why such behavior would be expected for a Peierls transition. In the low temperature region the crystal acts like a small gap semiconductor for which the –T−2 dependence of Δρ/ρ is easily understood. We note that the peak in the magnetoresistance at 52.8 K strongly suggests that the electronic energy gap goes to zero at this temperature. One is then led to conclude that the decrease in the conductivity between 58 and 53 K is due to resistive fluctuations above the metal–insulator transition.

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Effect of external magnetic field on the co-existence of superconductivity and antiferromagnetism in rare earth nickel borocarbides (RNi2B2C)

International Journal of Modern Physics B ◽

10.1142/s0217979216500442 ◽

2016 ◽

Vol 30 (08) ◽

pp. 1650044

Author(s):

Salila Das ◽

Prakash Chandra Padhi

Keyword(s):

Magnetic Field ◽

Rare Earth ◽

External Magnetic Field ◽

Energy Gap ◽

Density Wave ◽

Spin Density Wave ◽

Mean Field ◽

Antiferromagnetic Order ◽

Superconducting Energy Gap ◽

Nickel Borocarbides

In this paper, we have studied the effect of external magnetic field in the co-existing phase of superconducting and antiferromagnetism (AFM) of rare earth nickel borocarbides. The AFM in these systems might have originated due to both localized “f” electrons as well as itinerant electrons which are responsible for conduction. On the other hand, superconductivity (SC) is due to spin density wave, arising out of Fermi surface instability. The AFM order is mostly influenced by hybridization of the “f” electron with the conduction electron. Here, we have obtained the dependence of superconducting energy gap as well as staggered magnetic field on temperature T and energy [Formula: see text] in a framework based on mean field Hamiltonian using double time electron Green’s function. We have shown in our calculation the effect of external magnetic field on superconducting and antiferromagnetic order parameters for [Formula: see text] in the presence of hybridization. The ratio of the calculated effective gap and [Formula: see text] is close to BCS value which agrees quite well with experimental results.

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GIBBS ENTROPY APPROACH TO THE REALIZATION OF QUBITS AND QUTRITS

International Journal of Modern Physics B ◽

10.1142/s0217979213470061 ◽

2013 ◽

Vol 27 (29) ◽

pp. 1347006

Author(s):

CLAUDIA M. SARRIS ◽

ARACELI N. PROTO ◽

F. BARY MALIK

Keyword(s):

Magnetic Field ◽

Phase Transition ◽

Density Matrix ◽

Specific Heat ◽

Mean Field Theory ◽

Mean Field ◽

Maximum Entropy Principle ◽

Strongly Correlated ◽

Expectation Values ◽

Gibbs Entropy

We investigate, in this paper, the possibilities of generating qubits and qutrits in strongly correlated systems described by a modified of Hubbard Hamiltonian. Out of the complete set of commutating operators that form a close Lie algebra with this Hamiltonian, one can generate a particular operator, the expectation values of which, with respect to the density matrix generated from the Gibbs entropy by Maximum Entropy Principle (MEP), are 0 and ±1 near a particular temperature. This density matrix is generated by the superposition of highly coherent two-electronic states, analogous to the BCS ones. The concurrent existence of the expectation values of 0, +1 and -1 of this operator with respect to the density matrix occurs near the phase transition of aligned states to anti-aligned states. These are qutrits, which in the absence of a magnetic field reduces to qubits. We also present the general uncertainty principle (GUP) valid for the set of these operators, evaluate its value for specific heat, and examine the behavior of the specific heat and the related GUP as a function of the temperature. This temperature dependence of the specific heat, exhibits the expected trend of phase transition near the transition temperature. For the chosen Hamiltonian, we present the derivation of the postulate of Weiss' mean field theory. This relation points to the fact that to generate qubits and qutrits for the system investigated here, it must have an intrinsic magnetic field and be a strongly correlated system such as manganites. This investigation further points to the fact that the qutrits gate may be a suitable quantum computing algorithm for systems with intrinsic magnetic and applied electromagnetic fields, since in the presence of such fields z-projections of the state with spin-1 are no longer degenerate. This investigation establishes that the thermodynamical evolution of fermion pair in the presence of an interaction with its environment are different for qubits and qutrits, particularly in the presence of an internal and external magnetic field and possibly for the general case of electro-magnetic field.

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