Field Induced Spin Density Wave Research Articles

Two rapid oscillations in the magnetoresistance in the field-induced spin-density-wave state of(TMTSF)2ClO4

We report a systematic study of longitudinal and transverse magnetoresistance in the quasi-one-dimensional organic conductor $(\mathrm{TMTSF}{)}_{2}{\mathrm{ClO}}_{4}.$ We found two distinctly different quantum (rapid) oscillations (RO's) at different temperature regions in the field-induced spin-density-wave (FISDW) phase. For temperature sweeps in a fixed field, a resistance peak is observed at ${T}^{*}$ which depends on the field. Surprisingly, the type of RO is correlated with ${T}^{*}(H).$ The difference between two oscillations leads us to establish subphases in the main FISDW phase of $(\mathrm{TMTSF}{)}_{2}{\mathrm{ClO}}_{4}.$ We also found the low-field boundary of McKernan's 3.5 K phase from a sudden increase of resistance. Our results conclude that the separate SDW transition on each pair of the Fermi surfaces is possibly responsible for subphases in the FISDW phase.

Quantum Hall effect and anomalous transport in (TMTSF)2PF6

Under low temperatures and high magnetic fields, quasi-one dimensional organic conductor (TMTSF) 2 PF 6 exhibits a series of transitions to field-induced spin density wave (FISDW). Slightly above the onset of superconductivity in (TMTSF) 2 PF 6 , we observe a series of intervening phases that interrupt the sequence of FISDW that gives rise to the quantum Hall effect. These phases can be identified either as negative quantum numbered FISDW states or a puzzling arboresecent phase. Detailed study of the QHE in (TMTSF) 2 PF 6 reveals that the transport in the FISDW phases is dominated by anomalous longitudinal resistivities pzz and pyy that remain finite at low temperatures. While the quantization of σxy is not adversely affected at high magnetic fields, the transport in the intermediate magnetic field remains complicated. In addition, the conductivity along applied magnetic field, σ zz , cannot be easily understood in terms of three-dimensional QHE and is suggestive of the importance of inter-layer coupling.

Quantum oscillations in(DMET−TSeF)2AuCl2

We report magnetoresistance measurements to 33 T at low temperatures in dimethil(ethylendithio)tetraselenafulvalene ${(\mathrm{D}\mathrm{M}\mathrm{E}\mathrm{T}\ensuremath{-}\mathrm{T}\mathrm{S}\mathrm{e}\mathrm{F})}_{2}{\mathrm{AuCl}}_{2},$ an organic conductor with a strictly quasi-one-dimensional electronic structure at low temperatures. Magnetic field induced spin-density wave (FISDW) transitions, similar in origin to those observed in the Bechgaard salts, are investigated vs temperature and tilted magnetic field. Rapid oscillations (RO) of about 300 T are detected in this material, but only in the FISDW states. We conclude from this study that the reconstruction of a one-dimensional Fermi surface is a necessary condition for the RO phenomena to occur, and we describe the form of the resulting electronic structure.

1H NMR studies in the regime of the field-induced spin-density wave phases of (TMTSF)2PF6

We report 1 H proton spin-lattice relaxation measurements T l -1 on pressurized (TMTSF) 2 PF 6 in high magnetic fields. Maxima in T l -1 identify the phase transition to the field-induced spin-density wave (FISDW) state. Fluctuation effects are evident at temperatures above the transition, and vanish continuously in strength as the field is lowered to the critical field B c for the onset of the FISDW cascade.

Quantum Hall transitions in field-induced spin density systems

Field-induced spin density wave (FISDW) systems exhibit coexistence phases between well-defined Quantum Hall plateaux phases with even integers 2 N and 2 N′. We show that a disordered coexistence region accounts for the observed peaks in the longitudinal reisitivity as the field varies between plateaux. It also results in a random spin mixing which yields two energy-split extended states. The longitudinal resistance is expected to show two peaks with a temperature ( T) dependent width ∼ T κ . The peak width should saturate below the non-nesting interlayer coupling of ≈40 mK.

High field Hall effect in (DMET-TSeF) 2AuCl 2

The Hall effect of the quasi one-dimensional system (DMET-TSeF) 2AuCl 2 is reported at high fields where the system is in the FISDW (Field Induced Spin Density Wave) state. The Hall voltage shows similar but different behavior to those observed in the famous TMTSF system. The Hall voltages show step like behavior, but they are not clearly quantized. The voltage disappears above 18 T, and not the inverses of the FISDW boundary fields but the squares of them seem to show linear dependence to the phase indices n. The absolute values of the Hall voltages at the corresponding phase indices are about one tenth of the values observed in TMTSF system. Moving FISDW states have been proposed to understand the differences.

Negative hall plateaus in (TMTSF) 2PF 6 revisited

We have made a detailed study of the negative Hall plateaus associated with the magnetic field induced spin density waves (FISDW) in (TMTSF) 2PF 6. A series of negative dips in Hall effect, dispersed among the cascade of FISDW states, generate an intriguing sequence of FISDW transitions. Comparison of positive and negative Hall plateaus shows much similarity between the two class of FISDW states. The observed sequence of transitions is discussed in light of the recently proposed explanations for the negative Hall plateaus.

High-field electrodynamic investigation of (TMTSF) 2ClO 4

We have used a millimeter-wave technique to probe the complex AC conductivity of (TMTSF) 2ClO 4 in fields to 30 tesla. The fieldinduced-spin-density-wave (FISDW) transitions are clearly seen at low temperatures and low fields, as are the rapid oscillations at higher fields. In addition, we see evidence for a collective pinning mode of the FISDW at high fields.

Quantum hall effect and edge states in (TMTSF) 2PF 6

Study of high quality (TMTSF) 2PF 6 crystals reveals that the quantum Hall effect seen in the field-induced spin density wave states is accompanied by nearly vanishing longitudinal magnetoresistance. Motivated by these findings, we examine whether there are current carrying edge states associated with the quantum Hall effect in the (TMTSF) 2X Bechgaard salts. Measurements of in-plane and out-plane resistivities, R xx and R zz , and 2 and 4-terminal resistance suggest that the transport in the Bechgaard salts is dominated by the bulk and that it is difficult to separate the contribution from the edge states.

Negative Hall plateaus and quantum Hall effect in(TMTSF)2PF6

We present our study of negative Hall plateaus associated with the magnetic-field-induced spin-density waves (FISDW). Slightly above the the pressure necessary to stabilize superconductivity, the quantum Hall effect associated with the field-induced spin density waves is interrupted by several negative Hall plateaus and an in-between phase. Quantizations of the negative Hall plateaus suggests that these states may be identified as FISDW states with negative quantum numbers. The in-between phase occurs from splitting of a phase boundary deep inside the FISDW diagram and is reminiscent of the previously suggested arborescence.

Summary

Summary

High Field Phase Diagram in (TMTSF) 2ClO 4 under Anion Ordering

We study the ordered states of the field induced spin density wave (FISDW) in the presence of an anion ordering potential at zero and finite temperature self-consistently. We obtain a new FISDW state stabilized in a strong potential region, by which we can explain recently obtained phase diagram of (TMTSF) 2 ClO 4 . The anomalous behavior of the so-called rapid oscillation in the transport and thermodynamics quantities is attributable to the new FISDW state.

Magnetoroton modes of the ultraquantum crystal: Numerical study

The Field Induced Spin Density Wave phases observed in quasi-one-dimensional conductors of the Bechgaard salts family under magnetic field exhibit both Spin Density Wave order and a Quantized Hall Effect, which may exhibit sign reversals. The original nature of the condensed phases is evidenced by the collective mode spectrum. Besides the Goldstone modes, a quasi periodic structure of Magneto-Roton modes, predicted to exist for a monotonic sequence of Hall Quantum numbers, is confirmed, and a second mode is shown to exist within the single particle gap. We present numerical estimates of the Magneto-Roton mode energies in a generic case of the monotonic sequence. The mass anisotropy of the collective mode is calculated. We show how differently the MR spectrum evolves with magnetic field at low and high fields. The collective mode spectrum should have specific features, in the sign reversed "Ribault Phase", as compared to modes of the majority sign phases. We investigate numerically the collective mode in the Ribault Phase.

Field-induced spin-density-wave transitions and rapid oscillations observed in the microwave surface impedance of(TMTSF)2ClO4

We report microwave surface impedance measurements performed in the relaxed state of the quasi-one-dimensional organic conductor $(\mathrm{TMTSF}{)}_{2}{\mathrm{ClO}}_{4}$ at 16.5 GHz in a magnetic field applied along the hard axis ${(c}^{*})$ direction. The transition from the metallic to the field-induced spin-density-wave (FISDW) state is not as sharp as it is generally observed in the dc regime, but the phase diagram is in very good agreement with existing data. An enhanced ac conductivity is measured in the FISDW phases, which should reflect the contribution of the collective mode. The rapid oscillations of the microwave magnetoresistivity appear in both the metallic state and/or in the FISDW phase. The deduced frequency (260 T) and the temperature dependence of the rapid oscillation amplitude in the normal and condensed states are consistent with reported dc results. A frequency dampening of the amplitude that is different in the two phases is, however, observed compared to dc data; its possible origin is discussed and confirms the different origin of the two mechanisms.

Field-Induced Spin Density Wave in Periodic Potential

We study the Field-Induced Spin Density Wave in the presence of the periodic potential which is treated non-perturbatively. We obtain that both even and odd subphases weakly depend on the magnetic field in the strong potential case, while in the perturbation only even subphases strongly depend on the magnetic field. We discuss the recently reported phase diagram in (TMTSF) 2 ClO 4 .

Theory of the High Field Phase in (TMTSF)2ClO4under Anion Ordering

Stimulated by a recent experiment on (TMTSF) 2 ClO 4 , reporting a new phase diagram with a first order transition line at the high field, the field induced spin density wave (FISDW) states are reexamined under the anion ordering. It is found that a new type of FISDW state, which differs from that described by the so-called standard theory, is stabilized. We interpret the first order line as arising from a transition between the new state and the standard one when H is varied.

Temperature and magnetic field dependences of rapid oscillations in field induced spin-density-wave phase for (TMTSF) 2ClO 4

Magnetoresistance has been measured in the field induced spin-density-wave (FISDW) phase for (TMTSF) 2ClO 4. For a well relaxed single crystal, the a axis magnetoresistance is found to have a sharp maximum in the final FISDW phase. The field where the magnetoresistance has a maximum is 7.5T for T=1.6K and increases with increasing temperature. Anomalous temperature and magnetic field dependences of the rapid oscillations near the FISDW transition field are reported.

Quantum Hall transitions in (TMTSF)2PF6.

We have studied the temperature dependence of the integer quantum Hall transitions in the molecular crystal (TMTSF)$_2$PF$_6$. We find that the transition width between the quantum Hall plateaus does not exhibit the universal power-law scaling behavior of the integer quantum Hall effect observed in semiconducting devices. Instead, the slope of the $\rho_{xy}$ risers, $d\rho_{xy}/dB$, and the (inverse) width of the $\rho_{xx}$ peaks, $(\Delta B)^{-1}$, show a BCS-like energy gap temperature dependence. We discuss these results in terms of the field-induced spin-density wave gap and order parameter of the system.

The Quantum Hall Effect of Field Induced Spin Density Wave Phases: the Physics of the Ultra Quantum Crystal

The Quantum Hall Effect of Field Induced Spin Density Wave Phases is accounted for within a weak coupling theory which assumes that in the relevant low temperature part of the phase diagram the quasi one dimensional conductor is well described by Fermi liquid theory. Recent experimental results show that sign inversion of the Hall Plateaux takes place all the way down from the instability line of the normal state. The Quantum Nesting model, when it takes into account small perturbations away from perfect nesting, describes well not only the usual sequence of Hall plateaux, but also the anomalies connected with sign inversion of the Hall Effect. Experimental observation of de-doubling of sub-phase to sub-phase transition lines suggests that superposition of SDW order parameters occurs in some parts of the phase diagram. The collective excitations of the Ultra Quantum Crystal have a specific magneto-roton structure. The SDW case exhibits,apart from the usual spin waves, topological excitations which are either skyrmions or half skyrmions. It is suggested that magneto-rotons may have been observed some years ago in specific heat experiments.

Field Induced Spin Density Waves

The Field Induced Spin Density Waves (FISDWs) found in organic conductors represent a unique series of transitions which meld the one-dimensional physics of the Peierls instability with the two-dimensional physics of the Quantum Hall Effect. This paper presents a pedagogical introduction to the FISDW's in the Bechgaard salts, along with recent experimental results on related high magnetic field phenomena.