Electron heating in a multiple-quantum-well structure below 1 K

Wennberg, A. K. M.; Ytterboe, S. N.; Gould, C. M.; Bozler, H. M.; Klem, John F.; Morkoç̌, H.

doi:10.1103/physrevb.34.4409

Cited by 72 publications

(53 citation statements)

References 8 publications

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“…It is natural to suspect that the electron system gets heated as a consequence of weak electron-phonon coupling at ultra-low temperatures and that the entropy is transferred to the nuclei in case a strong interaction between the electron spins and nuclear spins exists. The current induced electron heating has been detected previously in many systems [50][51][52][53], but to the best of our knowledge, the electron heating effects at ν = 1/2 have not been studied systematically. At ν = 1/2, the nuclear spin system near the 2DES has only one, but very effective way interacting with the environment, namely the spin flip-flop process via the Fermi contact hyperfine interaction.…”

Section: B Current Induced Effect On Electron Transport Propertiesmentioning

confidence: 90%

Current-induced nuclear spin depolarization at Landau level filling factorν=1/2

Umansky

Klitzing

et al. 2012

Phys. Rev. B

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In this work we demonstrate that significant changes in electron temperature and nuclear spin polarization can be created by applying an electric current in a 2-dimensional electron system at Landau level filling factor ν = 1/2. The current induced effects on nuclear spins can be attributed to electron heating and the efficient coupling between the nuclear and electron spin systems at ν=1/2. The electron temperature, elevated by the current, can be measured with a thermometer based on the measurement of the nuclear spin relaxation rate. The electron temperature is found to be proportional to the square root of the current density at ν = 1/2. Electron spin transitions at ν = 2/3 and 1/2 are utilized for the measurement of the current induced changes in nuclear spin polarization. Consistent results are obtained from these two different methods of nuclear magnetometry. The finite thickness of the electron wavefunction is found to be important for evaluation of the nuclear spin polarization even in a narrow quantum well. The nuclear spin polarization follows a Curie law dependence on the electron temperature. This work also allows us to evaluate the electron g-factor in high magnetic fields as well as the polarization mass of composite fermions.

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Section: B Current Induced Effect On Electron Transport Propertiesmentioning

confidence: 90%

Current-induced nuclear spin depolarization at Landau level filling factorν=1/2

Umansky

Klitzing

et al. 2012

Phys. Rev. B

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“…This current could be due to defects such as interstitial electrons moving in a Bloch energy band created by the periodic potential of the electrons of the WS. In the metallic state 60 fW does not cause self-heating [27], but the effect of such a dissipated power on the WS is not known. Nonetheless self-heating on this branch of the I-V characteristic is unlikely since at a fixed B the measured V T is not T independent even at the lowest Ts.…”

Section: Prl 98 066805 (2007) P H Y S I C a L R E V I E W L E T T E mentioning

confidence: 99%

Astability and Negative Differential Resistance of the Wigner Solid

Csáthy

Tsui

Pfeiffer³

et al. 2007

Phys. Rev. Lett.

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We report an unusual breakdown of the magnetically induced Wigner solid in an exceptional two-dimensional electron gas. The current-voltage characteristic is found to be hysteretic in the voltage biased setup and has a region of negative differential resistance in the current biased setup. When the sample is current biased in the region of negative differential resistance, the voltage on and the current through the sample develop spontaneous narrow band oscillations.

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“…Cooling the electron system to ultra-low temperatures is a formidable task, since the electron-phonon coupling between the 2DES and its host lattice decreases precipitously with decreasing temperature [4,15]. An earlier experiment on ν = 5/2 [4] reached an electron temperature, T e , of only 9 mK in spite of a bath temperature of T b ∼ 0.5 mK.…”

mentioning

confidence: 99%

“…The resistance of the strongly T -dependent R xx peak at 3.75 T in Fig.1 was used as an internal thermometer for the electron temperature, T e , assuming T e = T b at higher T b and in the limit of low current. The T e vs I data fit the expected T 5 -relationship [4,15], ln(I 2 )= const + ln(T is in nA, T in mK and const = -7.5. At T b = 8.0 mK and 1 nA current it yields T e = 8.05 mK, sufficiently close to T b for the difference to be negligible.…”

mentioning

confidence: 99%

Exact Quantization of the Even-Denominator Fractional Quantum Hall State atν=5/2Landau Level Filling Factor

et al. 1999

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We report ultra-low temperature experiments on the obscure fractional quantum Hall effect (FQHE) at Landau level filling factor ν = 5/2 in a very high mobility specimen of µ = 1.7 × 10 7 cm 2 /Vs. We achieve an electron temperature as low as ∼ 4 mK, where we observe vanishing Rxx and, for the first time, a quantized Hall resistance, Rxy = h/(5/2e2 ) to within 2 ppm. Rxy at the neighboring odd-denominator states ν = 7/3 and 8/3 is also quantized. The temperature dependences of the Rxx-minima at these fractional fillings yield activation energy gaps ∆ 5/2 = 0.11 K, ∆ 7/3 = 0.10 K, and ∆ 8/3 = 0.055 K.PACS Numbers: 73.40Hm Electrons in two-dimensional systems at low temperatures and in the presence of an intense magnetic field condense into a sequence of incompressible quantum fluids with finite energy gaps for quasiparticle excitation, termed collectively the fractional quantum Hall effect (FQHE) [1]. These highly correlated electronic states occur at rational fractional filling ν = p/q of Landau levels. Their characteristic features in electronic transport experiments are vanishing resistance, R xx , and exact quantization of the concomitant Hall resistance, R xy , to h/(p/qe 2 ). Over the years, a multitude of FQHE states have been discovered -all q's being odd numbers. The only known exceptions are the states at half-filling of the second Landau level ν = 5/2 (=2+1/2) and ν = 7/2 (=3+1/2) [2-4]. Half-filled states in the lowest Landau level show no FQHE, whereas half-filled states in still higher Landau levels exhibit yet unresolved anisotropies [5]. Recent experiments in tilted magnetic field even seem to hint at a connection between the ν = 9/2 state and the state at ν = 5/2 [6].The origin of the ν = 5/2 and 7/2 states remains mysterious. Observation of odd-denominator FQHE states is intimately connected to the anti-symmetry requirement for the electronic wave function. An early, socalled hollow-core model [7] for the FQHE at ν = 5/2 and 7/2, which takes explicitly into account aspects of the modified single-particle wave functions of the second Landau level, arrived at a trial wave function. However, for a Coulomb Hamiltonian its applicability is problematic [8,9].With the advent of the composite fermion (CF) model [10] the existence of exclusively odd-denominator FQHE states is traced back to the formation of Landau levels of CFs emanating from even-denominator fillings, such as the sequence ν = p/(2p ± 1) from ν = 1/2. Evendenominator fillings themselves represent Fermi-liquid like states, resulting from the attachment of an even number of magnetic flux quanta to each electron. The obvious conflict between this theory and experiment at ν = 5/2 is resolved by invoking a CF-pairing mechanism [11][12][13][14]. In loose analogy to the formation of Cooper pairs in superconductivity such pairing creates a gapped, BCS-like ground state at ν = 5/2, called a "Pfaffian" state, which displays a FQHE. Indeed, an exact numerical diagonalization calculation by Morf [9] favors the Pfaffian state.The experimental si...

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Electron heating in a multiple-quantum-well structure below 1 K

Cited by 72 publications

References 8 publications

Current-induced nuclear spin depolarization at Landau level filling factorν=1/2

Current-induced nuclear spin depolarization at Landau level filling factorν=1/2

Astability and Negative Differential Resistance of the Wigner Solid

Exact Quantization of the Even-Denominator Fractional Quantum Hall State atν=5/2Landau Level Filling Factor

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