Biomedical subjects

D Belitz

Publications and source records attributed to D Belitz.

At least 19 recordsLinked to original sources

PubMed2006

Blue quantum fog: chiral condensation in quantum helimagnets.

It is shown that a condensation transition involving a chiral order parameter can occur in itinerant helimagnets, in analogy to the transition between the isotropic phase and the phase known as blue fog or blue phase III in cholesteric liquid crystals. It is proposed that such a transition is the explanation for recent neutron scattering results in MnSi. Predictions are made that will allow for experimental tests of this proposal.

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PubMed2004

Spontaneous flux lattices in ferromagnetic spin-triplet superconductors.

A theory is developed for the spontaneous vortex lattice that is expected to occur in the ferromagnetic superconductors ZrZn2, UGe2, and URhGe, where the superconductivity is likely of the spin-triplet nature. The long-wavelength fluctuations of this spontaneous flux lattice are predicted to be huge compared to those of a conventional flux lattice, and to be the same as those for spin-singlet ferromagnetic superconductors. It is shown that these fluctuations lead to unambiguous experimental signatures which may provide the easiest way to observe the spontaneous flux lattice.

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PubMed2004

Breakdown of the perturbative renormalization group at certain quantum critical points.

It is shown that the presence of multiple time scales at a quantum critical point can lead to a breakdown of the loop expansion for critical exponents, since coefficients in the expansion diverge. Consequently, results obtained from finite-order perturbative renormalization-group treatments may not be an approximation in any sense to the true asymptotic critical behavior. This problem manifests itself as a nonrenormalizable field theory, or, equivalently, as the presence of a dangerous irrelevant variable. The quantum ferromagnetic transition in disordered metals provides an example.

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PubMed2004

Signatures of pairing mechanisms and order parameters in ferromagnetic superconductors.

Two predictions are made for properties of the ferromagnetic superconductors discovered recently. The first one is that spin-triplet, p-wave pairing in such materials will give the magnons a mass inversely proportional to the square of the magnetization. The second one is based on a specific mechanism for p-wave pairing and predicts that the observed broad anomaly in the specific heat of URhGe will be resolved into a split transition with increasing sample quality. These predictions will help discriminate between different possible mechanisms for ferromagnetic superconductivity.

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PubMed2002

Fluctuation-driven quantum phase transitions in clean itinerant ferromagnets.

The quantum phase transition in clean itinerant ferromagnets is analyzed. It is shown that soft particle-hole modes invalidate Hertz's mean-field theory for d< or =3. A renormalized mean-field theory predicts a fluctuation-induced first order transition for 1<d< or =3, whose stability is analyzed by renormalization group techniques. Depending on microscopic parameter values, the first order transition can be stable, or be preempted by a fluctuation-induced second order transition. The critical behavior at the latter is determined. The results are in agreement with recent experiments.

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PubMed2001

Strong enhancement of superconducting T(c) in ferromagnetic phases.

It is shown that the critical temperature for spin-triplet, p-wave superconductivity mediated by spin fluctuations is generically much higher in a Heisenberg ferromagnetic phase than in a paramagnetic one, due to the coupling of the magnons to the longitudinal magnetic susceptibility. Together with the tendency of the low-temperature ferromagnetic transition in very clean Heisenberg magnets to be of first order, this qualitatively explains the phase diagram recently observed in UGe(2).

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PubMed2000

Transport anomalies and marginal-fermi-liquid effects at a quantum critical point

The conductivity and the tunneling density of states of disordered itinerant electrons in the vicinity of a ferromagnetic transition at low temperature are discussed. Critical fluctuations lead to nonanalytic frequency and temperature dependencies that are distinct from the usual long-time tail effects in a disordered Fermi liquid. The crossover between these two types of behavior is proposed as an experimental check of recent theories of the quantum ferromagnetic critical behavior. In addition, the quasiparticle properties at criticality are shown to be those of a marginal Fermi liquid.

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PubMed2000

Annealed disorder, rare regions, and local moments: A novel mechanism for metal-insulator transitions

It is shown that, for noninteracting electron systems, annealed magnetic disorder leads to a new mechanism, and a new universality class, for a metal-insulator transition. The transition is driven by a vanishing of the thermodynamic density susceptibility rather than by localization effects. The critical behavior in d = 2+epsilon dimensions is determined, and the underlying physics is discussed. It is further argued that annealed magnetic disorder, in addition to underlying quenched disorder, describes local magnetic moments in electronic systems.

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PubMed1996