Bias-voltage-induced phase transition in bilayer quantum Hall ferromagnets

Joglekar, Yogesh N.; MacDonald, Allan H.

doi:10.1103/physrevb.65.235319

Cited by 42 publications

(66 citation statements)

References 28 publications

(62 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is well known that the 111 wavefunction can easily accommodate layer imbalance. 60 In the paired-CF phase, on the other hand, this type of perturbation (like a Zeeman field in a traditional superconductor) is clearly pair breaking since the ↑ and ↓ Fermi surfaces would be of different sizes (Although in principle more exotic types of pairing could be constructed to accommodate such differences). A much more interesting question to ask is what happens in the regime where there are both CFs and CBs.…”

Section: Discussionmentioning

confidence: 99%

Trial wave functions forν=12+12quantum Hall bilayers

Möller¹,

Simon²,

Rezayi

2009

Phys. Rev. B

View full text Add to dashboard Cite

Quantum Hall bilayer systems at filling fractions near ν = 1 2 + 1 2 undergo a transition from a compressible phase with strong intralayer correlation to an incompressible phase with strong interlayer correlations as the layer separation d is reduced below some critical value. Deep in the intralayer phase (large separation) the system can be interpreted as a fluid of composite fermions (CFs), whereas deep in the interlayer phase (small separation) the system can be interpreted as a fluid of composite bosons (CBs). The focus of this paper is to understand the states that occur for intermediate layer separation by using trial variational wavefunctions. We consider two main classes of wavefunctions. In the first class, previously introduced in Möller et al. (2003)] and generalizes the idea of pairing wavefunctions by allowing the CFs also to be replaced continuously by CBs. This generalization allows us to construct exceedingly good wavefunctions for interlayer spacings of d ℓ 0 , as well. The accuracy of the wavefunctions discussed in this work, compared with exact diagonalization, approaches that of the celebrated Laughlin wavefunction.

show abstract

Section: Discussionmentioning

confidence: 99%

Trial wave functions forν=12+12quantum Hall bilayers

Möller¹,

Simon²,

Rezayi

2009

Phys. Rev. B

View full text Add to dashboard Cite

show abstract

“…Joglekar and MacDonald find that the collective mode spectrum stiffens and the critical d / ᐉ increases quadratically with ⌬ v , the splitting between the single-particle ground states in the two quantum wells. Since the interlayer capacitance in the T = 1 coherent phase is only slightly renormalized, 26 ⌬ v is essentially proportional to ⌬N / N T . The dashed line in Fig.…”

mentioning

confidence: 99%

“…[24][25][26] Joglekar and MacDonald 26 offer a quantitative prediction for the shape of the phase boundary. In their Hartree-Fock theory the magneto-roton minimum in the collective mode spectrum of the strongly coupled phase deepens as d / ᐉ increases, signaling incipient instability against charge density wave formation.…”

mentioning

confidence: 99%

Onset of interlayer phase coherence in a bilayer two-dimensional electron system: Effect of layer density imbalance

et al. 2004

View full text Add to dashboard Cite

Tunneling and Coulomb drag are sensitive probes of spontaneous interlayer phase coherence in bilayer two-dimensional electron systems at total Landau level filling factor T = 1. We find that the phase boundary between the interlayer phase coherent state and the weakly coupled compressible phase moves to larger layer separations as the electron density distribution in the bilayer is imbalanced. The critical layer separation increases quadratically with layer density difference. Bilayer two-dimensional electron systems (2DES) are most interesting when the separation between the layers is comparable to the average distance between electrons in the individual layers. Interlayer Coulomb interactions are then just as important as intralayer ones and the system supports collective phases that do not exist in the individual layers. 1 A particularly interesting example occurs when a magnetic field B is applied perpendicular to the layers and the total density N T = N 1 + N 2 of electrons in the system equals the degeneracy eB / h of the lowest spin-resolved Landau level produced by the field. In this case the total Landau level filling factor T = 1 + 2 = hN T / eB = 1. Beyond exhibiting a quantized Hall effect (QHE) when electrical currents flow in parallel through the two layers, 2 this many-body phase displays a variety of fascinating phenomena associated with observables which are antisymmetric in the layer degree of freedom. For example, a giant enhancement of the zero bias interlayer tunneling conductance has been observed, 3 as has the vanishing of both the longitudinal and Hall resistances of the system when equal but oppositely directed currents flow in the two layers. 4,5 These findings strongly support the idea that the ground state of the system is a Bose condensate of phase coherent interlayer excitons.As the separation between the layers is increased, the excitonic phase weakens and a poorly understood transition to a state exhibiting none of the above properties occurs. At very large layer separation a balanced bilayer system (i.e., one in which N 1 = N 2 and thus 1 = 2 =1/2) may be regarded as two independent compressible composite fermion liquids. 6 However, near the critical layer separation the situation is much less clear. Indeed, it is not known what the order of the transition is nor whether intermediate phases exist between the excitonic phase and the weakly coupled composite fermion fluid. Recent experiments 7 have shown a strong enhancement of the longitudinal Coulomb drag in the transition region which has been interpreted 8 in terms of phase separation induced by static disorder.If the bilayer system is imbalanced, but remains at T =1, the spectrum of possible phases widens further. At large layer separation, both compressible (e.g., 1 =1/4, 2 =3/4) and incompressible (e.g., 1 =1/3, 2 =2/3) possibilities exist. At small separations, deep in the excitonic phase, small layer imbalances are not expected to be qualitatively important, since this state is characterized by a broken U͑1͒ symmetry in wh...

show abstract

“…Theoretical dispersions ω(q) display characteristic magnetoroton (MR) minima at finite wave-vectors (q ∼ l −1 B ) that are due to excitonic binding terms of the Coulomb interactions in the neutral pairs [3,4]. It has been predicted that MRs can soften and create instabilities leading to quantum phase transitions that transform the ground-states into highly correlated electron phases [3,5,6,7,8,9].Coupled electron bilayers at total Landau level filling factor ν T =1 exhibit a rich quantum phase diagram due to the interplay of transition energies ∆ SAS across the tunneling gap with intra-and inter-layer interactions [5,8,10,11,12,13]. Interactions drive quantum phase transitions from the incompressible ferromagnetic quantized Hall phase, stable at low inter-layer spacing d or large ∆ SAS , to a compressible phase that results from the collapse of the many-body tunneling gap.…”

mentioning

confidence: 99%

Observation of Soft Magnetorotons in Bilayer Quantum Hall Ferromagnets

et al. 2003

View full text Add to dashboard Cite

Inelastic light scattering measurements of low-lying collective excitations of electron double layers in the quantum Hall state at total filling νT =1 reveal a deep magnetoroton in the dispersion of charge-density excitations across the tunneling gap. The roton softens and sharpens markedly when the phase boundary for transitions to highly correlated compressible states is approached. The findings are interpreted with Hartree-Fock evaluations that link soft magnetorotons to enhanced excitonic Coulomb interactions and to quantum phase transitions in the ferromagnetic bilayers.PACS numbers: 73.43. Lp, The quantum Hall states of the two-dimensional electron gas (2DEG) occur in high perpendicular magnetic fields that quantize the kinetic energy into discrete, highly-degenerate Landau levels (LLs). The energy scale for Coulomb interactions is here e 2 /ǫl B , where l B = hc/eB is the magnetic length and B the perpendicular magnetic field. The neutral quasiparticle-quasihole excitations carry the fingerprints of electron interactions [1,2]. Low-lying collective modes of energies ω(q) and in-plane wave vector q are linked to the condensation into highly correlated states that emerge in the presence of strong electron interactions. Theoretical dispersions ω(q) display characteristic magnetoroton (MR) minima at finite wave-vectors (q ∼ l −1 B ) that are due to excitonic binding terms of the Coulomb interactions in the neutral pairs [3,4]. It has been predicted that MRs can soften and create instabilities leading to quantum phase transitions that transform the ground-states into highly correlated electron phases [3,5,6,7,8,9].Coupled electron bilayers at total Landau level filling factor ν T =1 exhibit a rich quantum phase diagram due to the interplay of transition energies ∆ SAS across the tunneling gap with intra-and inter-layer interactions [5,8,10,11,12,13]. Interactions drive quantum phase transitions from the incompressible ferromagnetic quantized Hall phase, stable at low inter-layer spacing d or large ∆ SAS , to a compressible phase that results from the collapse of the many-body tunneling gap. In current theories the phase transitions are linked to soft roton instabilities in the charge-density-excitations (CDE) across the tunneling gap [5,8]. Within the Hartree-Fock framework the magnetoroton instability is related to intra-layer interactions that lead to large excitonic bindings between quasiparticles and quasiholes.Recent experimental studies of coupled electron double layers in ν T =1 ferromagnetic states focus on the very low ∆ SAS region of the phase diagram, where interlayer Coulomb correlations are important. These studies have displayed enhanced zero-bias inter-layer tunneling characteristics and anomalous quantized Hall drag [14,15,16]. These remarkable results are interpreted as evidence of a Goldstone mode in the incompressible phase and of condensation of the bilayers into many-body exciton phases. Experiments that probe dispersive collective excitations and their softening as a function of ∆ SAS and...

show abstract

Bias-voltage-induced phase transition in bilayer quantum Hall ferromagnets

Cited by 42 publications

References 28 publications

Trial wave functions forν=12+12quantum Hall bilayers

Trial wave functions forν=12+12quantum Hall bilayers

Onset of interlayer phase coherence in a bilayer two-dimensional electron system: Effect of layer density imbalance

Observation of Soft Magnetorotons in Bilayer Quantum Hall Ferromagnets

Contact Info

Product

Resources

About