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Register a new userMagnetic Field Dependent Behavior of the CDW ground state in Per2M(mnt)2 (M = Au, Pt)
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The Per2M(mnt)2 class of organic conductors exhibit a charge density wave (CDW) ground state below about 12 K, which may be suppressed in magnetic fields of order 20 to 30 T. However, for both cases of counter ion M(mnt)2 species studied (M = Au (zero spin) and M = Pt (spin 1/2)), new high field ground states evolve for further increases in magnetic field. We report recent investigations where thermopower, Hall effect, high pressure and additional transport measurements have been carried out to explore these new high field phases.
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Recently the authors discovered that the suppression of the charge density wave (CDW) ground states by high magnetic fields in the organic conductor series Per2M(mnt)2 is followed by additional high field, CDW-like phases. The purpose of this presentation is to review these compounds, to consider the relevant parameters of the materials that describe the manner in which the CDW ground state may undergo new field induced changes above the Pauli limit.
A finite transfer integral $t_a$ orthogonal to the conducting chains of a highly one-dimensional metal gives rise to empty and filled bands that simulate an indirect-gap semiconductor upon formation of a commensurate charge-density-wave (CDW). In contrast to semiconductors such as Ge and Si with bandgaps $sim 1$ eV, the CDW system possesses an indirect gap with a greatly reduced energy scale, enabling moderate laboratory magnetic fields to have a major effect. The consequent variation of the thermodynamic gap with magnetic field due to Zeeman splitting and Landau quantization enables the electronic bandstructure parameters (transfer integrals, Fermi velocity) to be determined accurately. These parameters reveal the orbital quantization limit to be reached at $sim 20$ T in (Per)$_2M$(mnt)$_2$ salts, making them highly unlikely candidates for a recently-proposed cascade of field-induced charge-density wave states.
Graf {it et al.} [Phys. Rev. Lett. {bf 93} 076406 (2004)] recently attributed features in the magnetic-field-dependent longitudinal resistance of (Per)$_2$Pt(mnt)$_2$ to a cascade of field-induced charge-density waves (FICDWs). Here we show that a quantitative magnetotransport analysis reveals orbital quantization to be absent, disproving the presence of FICDWs. Our data show that the conduction is instead dominated by the sliding CDW collective mode at low temperatures.
Graphene SU(4) quantum Hall symmetry is extended to SO(8), permitting analytical solutions for graphene in a magnetic field that break SU(4) spontaneously. We recover standard graphene SU(4) physics as one limit, but find new phases and new properties that may be relevant for understanding the ground state. The graphene SO(8) symmetry is found to be isomorphic to one that occurs extensively in nuclear structure physics, and very similar to one that describes high-temperature superconductors, suggesting deep mathematical connections among these physically-different fermionic systems.
Trivalent americium has a non-magnetic ($J$ = 0) ground state arising from the cancelation of the orbital and spin moments. However, magnetism can be induced by a large molecular field if Am$^{3+}$ is embedded in a ferromagnetic matrix. Using the technique of x-ray magnetic circular dichroism, we show that this is the case in AmFe$_2$. Since $langle J_z rangle$ = 0, the spin component is exactly twice as large as the orbital one, the total Am moment is opposite to that of Fe, and the magnetic dipole operator $langle T_{z} rangle$ can be determined directly; we discuss the progression of the latter across the actinide series.
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