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Keshav N. Shrivastava

Publications and source records attributed to Keshav N. Shrivastava.

At least 19 recordsLinked to original sources
arXiv2004

Comments on "Anomalous-Filling-Factor-Dependent Nuclear Spin Polarization in a 2D Electron System: Quantum Hall Effect" by J.H.Smet, K. von Klitzing et al, Phys. Rev. Lett. 92, 086802(2004)

We find that the nuclear-spin polarization has not been treated correctly. The references given are those of wrong papers. The credits assigned for discoveries are also not correct. Incorrect theories have been cited. The reference to the correct theory has been neglected. Because there are lots of good people, so they do not want to give reference to my papers even though they have not solved the problem of quantum Hall effect and we have.

cond-mat.mes-hall↗
arXiv2004

Comments on "Competition Between Fractional Quantum Hall Liquid ...", by G. Gervais, L. W. Engel, H. L. Stormer, D. C. Tsui, et al (cond-mat/0402169)

The quantum Hall effect in ultra-high mobility GaAs/AlGaAs has been measured and plateaus are found at many different fractions. The resistivity is quantized as ρ=h/ie^2 where i exhibits many different values. The fractions 5/3, 8/5, 11/7, 14/9, 17/11 fit the formula, i=3p\pm 2/(2p \pm 1) and it is claimed that 2p flux quanta are attached to the electron. The fractions 4/11, 7/11, 12/7, 13/8 and 15/11 do not fit the expression for i, even then the authors insist that flux quanta are attached to the electron and hence composite fermions (CF) are formed. We report that the interpretation of the experimental data in terms of CF is incorrect.

cond-mat.mes-hall↗
arXiv2003

Doubling of Landau levels in GaAs/AlGaAs heterostructures

Usually the Landau levels are given by (n+1/2)\hbarω_c with \hbarω_c=eB/mc. We find that there are clusters of electrons with localization so that the orbital angular momentum is not zero. There are interactions which transfer the electrons from {\it l}=0 to {\it l}\ne 0 so that there is doubling in the Landau levels with \hbarω_c= (1/2)g_\pmeB/mc where (1/2)g_\pm=({\it l}+(1/2)\pm s)/(2{\it l}+1) For s=\pm 1/2 two distinct values of ω_c appear whereas only one seems to be known in the literature. This is because only one value s=+1/2 is populated. When microwaves of a suitable frequency such as 13.1 GHz at a field of about 2.5 Tesla, are turned on, s=-1/2 also gets populated. For singlets s=0, (1/2)g_\pm=1/2 so that ω_c=(1/2)(eB/mc). This will double the number of oscillations in the resistivity as a function of magnetic field. This theory of doubling of the oscillations agrees with the experimental data on GaAs/AlGaAs.

cond-mat.mes-hall↗
arXiv2003

Microwave resonance in 2D Wigner crystals

Recent experimental measurements of the microwave absorption in the frequency range 1-4 GHz show peaks at several values of the filling factor,ν=nh/eB. Since the filling factor multiplies the magnetic field, it is similar to the Lande's splitting factor, g. By using both signs in j={\it l}\pm s, we obtain a formula for the splitting factor which is equivalent to obtaining the filling factor. The experimentally observed values of 6/5, 4/3, 7/5, 8/5, 5/3, 7/3 and 5/2 are in agreement with our formula provided that we propose that there are "electron clusters". The clusters have {\it l} and s values and vary in size. It is possible to interpret the filling factor as a fractional charge. When charge becomes zero, the transverse resistivity diverges so that large resistivity belongs to an insulator which is called a "Wigner crystal".

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arXiv2003

Clustering in quantum Hall effect: Spin-charge coupling

The effective fractional charges like 17/4 or 19/4 are explained by our angular momentum theory. These fractions do not arise from the odd denominator rule. Due to spin polarization for both of these along the magnetic field, these states are not the particle-hole conjugates. The idea of clustering first introduced in cond-mat/0303309 has been extended to atomic clusters which explain the oscillations in the kHz range. The effective charge is found to depend linearly on spin, i.e., charge \pm spin =1/2. This is a new spin-charge coupling relationship in a purely electronic system.

cond-mat.mes-hall↗
arXiv2003

Comments on `` Scattering of bunched fractionally charged quasiparticles" by Chung, Heiblem and Umansky, cond-mat/0305325

In the experiments, the quantity measurd is the product of the charge and the magnetic field from which fractional charge is deduced. There is no objection to measuring the fractional charge as long as it is remembered that the product of the charge and the field has been measured. So If the fraction came from the field rather than from the charge, the experiment will remain unaffected. There is no prescription about the mass splitting so there is no way to combine two masses into one. Therefore, the fractional charge can be obtained by changing the state of the quasiparticle without splitting, then there is no bunching.

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arXiv2003

New Resonances Along with Cyclotron Resonance in Heterostructures

The usual cyclotron resonance occurs at ω_c=eB/m*c which is independent of spin. The new resonances depend on spin. The new resonances occur at ω_{c\pm}=(1/2)g_{\pm}eB/m*c where (1/2)g_{\pm}= {\it l}+(1/2)\pm s/(2{\it l}+1). The energy in the centre of two new frequencies varies as the square root of the 2-dimensional electrons due to spin excess in the Gaussian model. The frequencies ω_{c\pm} are linearly proportional to the magnetic field except near crossing point where the linear combination of wave functions must be made.

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arXiv2003

Thermoelectric power in between two plateaus in quantum Hall effect

We have considered the response at two energies corresponding to two plateaus in the quantum Hall effect. Since the thermoelectric power involves the derivative of conductivity with respect to energy, we introduce the concept of a line width and hence an activation energy. We then use the Hall conductivity to define the thermoelectric power at the centre of two plateaus, which is found to vary monotonically as T^2 at low temperatures with fixed magnetic field. At elivated temperatures, the thermoelectric power varies as T(exp-Δ/k_BT).

cond-mat.mes-hall↗
arXiv2003

Quantum Gunn effect: Zero-resistance state in 2D electron gas

Usually the conductivity is quantized as the inverse of the resistivity, ρ=hc/ie^2, σ=ie^2/hc and the velocity versus the electric field is linear, v=μE where μis the mobility of the electrons.However,when the applied electric field exceeds a certain value, microwaves are emitted and the relation v=μE breaks down so that the velocity actually reduces as E increases. In this region, when magnetic field is applied, the conductivity quantizes like the magnetic field, i.e., in units of hc/e which is different from the usual quantization. Because of the flux quantization, the resistivity will touch zero in the region of high electric field. Factors like 4/5 arise due to new spin dependence of the effective charge.

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arXiv2003

Quasiparticles in quantum Hall effect: Smet's fractional charge

It has been pointed out by Smet that there are fractional-charge values which do not fit with their formula of composite fermions. We find that our formula predicts these fractional charges very well and in fact there exists a relationship between spin and charge of a quasiparticle.

cond-mat.mes-hall↗
arXiv2003

Comments on "Composite Fermion (CF) model of quantum Hall effect: Two-dimensional electron systems in high magnetic fields": S. S. Mandal, M. R. Peterson and J. K. Jain, Phys. Rev. Lett.90, 106403(2003)

The flux quanta attachment to the electrons creates composite fermions (CFs). The mass, the size and the density of the CF are inconsistent with real material. The sequence of fractional charges which suggest formation of CF agrees with the data but there are no monopoles in GaAs. Hence, the CF model is internally inconsistent. There are two possibilities. (1) The flux quanta are attached to the electrons. This is a theoretical possibility with nothing to do with any experiment ever performed within the last seventy five years. It will violate Maxwell equations and create unreal objects. (2) The CF give a sequence which is deduced from the experimental data and hence agrees with the data itself. In this case the masses of CF, the sizes and the densities are internally inconsistent.

cond-mat.mes-hall↗
arXiv2003

Fractional charge in electron clusters: Mani and von Klitzing data of quantum Hall effect- Part II

We have calculated the fractional charge of quasiparticles in a cluster of electrons. The 61 values have been calculated which are exactly the same as the measured values. In a previous eprint we have calculated 85 values which are the same as the measured values. Thus we have calculated 146 fractional charges. In the case of 61 values, we are able to determine the spin of the cluster and hence the number of electrons. The polarization in a magnetic field is determined. A new zero conductivity state is found which is the same as superresistivity, previously reported in our book. Anderson and Brinkman, cond-mat/0302129, have noted that frequencies like 5/4Ω_c do occur. We predict all fractional frequencies correctly.

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arXiv2003

Fractional charge in electron clusters: Interpretation of Mani and von Klitzing quantum Hall effect data

The charge of an electron in a cluster of n electrons is not ne but it is a fraction. We make many different clusters and calculate their charge per electron. We make 84 clusters and calculate the charge of an electron in these clusters. All of the 84 calculated values are exactly the same as found in the experimental measurements. The formulation is so good that all fractional charges if and when measured can be reduced to ${\it l}$ and $s$ values where the denominator in the fractional charge is simply 2{\it l}+1.

cond-mat.mes-hall↗
arXiv2003

Comments on "Mutually composite fermions in double layer quantum Hall systems", Jinwu Ye, cond-mat/0302558: Why is it wrong?

Jinwu Ye has shown that two flux quanta are attached in one layer while the electron is in the other layer to form a mutually composite fermion (MCF). This idea is based on an earlier idea that CF are formed by attaching two flux quanta to one electron. We find that the formation of MCF is unphysical and it can not be the basis of a new theory. Similarly, the CF are also unphysical objects and their Lorentz invariance is missing.

cond-mat.mes-hall↗
arXiv2003

Spin-dependent charge of quasiparticle clusters in quantum Hall effect: Interpretation of unsolved data of Pan, Stormer, Tsui, Pfeiffer, Baldwin and West

A state with two electrons has a charge of 1/2. The states of three electrons have quasiparticle charge of 4/11 and 5/13, the one with 5 electrons have quasiparticle charges of 4/13 and 6/17. The state with 7 elctrons exhibits quasiparticle charges of 5/17 and 12/17. When spin is reversed, the charge of the three-particle state changes from 4/11 to 7/11. These predicted results agree with the recent experimental measurements of Pan, Stormer, Tsui et al.

cond-mat.mes-hall↗
arXiv2003

Fractional Charge Experiments: What quantity is measured in quantum Hall effect or calculated by Laughlin?

We have examined the experiments performed by Goldman and Su, de-Picciotto et al, Samanadayar et al and Conforti et al in which it is claimed that a fractional charge of e/3 is found. In all of the measurements, the quantity measured is the product of the charge and the magnetic field but not the charge. It is possible to interpret that charge per unit area has been measured, where the area is the square of the magnetic length. This type of correction to Laughlin's result does not affect the exactness of the calculation. Anderson has suggested the extension of Laughlin's state to particles of charge 2/m or 3/m with m=odd integer. We find that the quasiparticle charge depends on the angular momenta, e_{eff}/e=({\it l}+(1/2)\pm s)/(2{\it l}+1) which agrees with the data. Therefore, Laughlin's 1/odd becomes an angular momentum so the charge depends on spin, s.

cond-mat.mes-hall↗
arXiv2003

Comments on "Gauge Theory of Composite Fermions:Particle-Flux Separation in Quantum Hall Systems" by I. Ichinose and Tetsuo Matsui, cond-mat/0210142 v2, 7 Feb. 2003

We find that the work of Ichinose requires far too many quasiparticles. As a result too many parameters are introduced to fit the mass of a composite fermion (CF) and hence experimentally, it will not be possible to identify all of such quasiparticles and their masses. Further, according to Ichinose, an electron decay should occur but it has not been found. It is much too unrealistic to expect an electron decay similar to the neutron decay. If the CF is really found it is not going to be relevent to the quantum Hall effect. Therefore, the composite fermion (CF) model of quantum Hall effect is not well founded and should be discarded.

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