Manohar Kumar

Ecole Normale Supérieure de Paris | ENS · Département de Physique

The non-Abelian state has garnered considerable interest in the field of fundamental physics and future applications in quantum computing. In this review, we introduce the basic ideas of constructing the non-Abelian states in various systems from 1D to 3D and discuss the possible approaches to detect these states, including the Majorana bound state...

A versatile nanowire system has enabled the hunt for particles that could be useful for quantum computers. The platform can be probed with two techniques simultaneously — minimizing the possibility of false-positive signals. Nanowire eliminates false-positive signals of quasiparticles.

We have studied 1/ f noise in critical current $$I_c$$ I c in h-BN encapsulated monolayer graphene contacted by NbTiN electrodes. The sample is close to diffusive limit and the switching supercurrent with hysteresis at Dirac point amounts to $$\simeq 5$$ ≃ 5 nA. The low frequency noise in the superconducting state is measured by tracking the variat...

We have measured magnetoresistance of suspended graphene in the Corbino geometry at magnetic fields up to B=0.15T, i.e., in a regime uninfluenced by Shubnikov–de Haas oscillations. The low-temperature relative magnetoresistance [R(B)−R(0)]/R(0) is strong, approaching 100% at the highest magnetic field studied, with a quite weak temperature dependen...

We have measured magnetoresistance of suspended graphene in the Corbino geometry at magnetic fields up to $B=0.15\,$T, i.e., in a regime uninfluenced by Shubnikov-de Haas oscillations. The low-temperature relative magnetotoresistance $[R(B)-R(0)]/R(0)$ amounts to $4000 B^2\% $ at the Dirac point ($B$ in Tesla), with a quite weak temperature depende...

Two-dimensional systems can host exotic particles called anyons whose quantum statistics are neither bosonic nor fermionic. For example, the elementary excitations of the fractional quantum Hall effect at filling factor $\nu=1/m$ (where m is an odd integer) have been predicted to obey abelian fractional statistics, with a phase $\varphi$ associated...

Looking for intermediate statistics Elementary particles in three dimensions are either bosons or fermions, depending on their spin. In two dimensions, it is in principle possible to have particles that lie somewhere in between, but detecting the statistics of these so-called anyons directly is tricky. Bartolomei et al. built a collider of anyons i...

In quantum nanoelectronics, time-dependent electrical currents are built from few elementary excitations emitted with well-defined wavefunctions. However, despite the realization of sources generating quantized numbers of excitations, and despite the development of the theoretical framework of time-dependent quantum electronics, extracting electron...

In quantum nanoelectronics, time-dependent electrical currents are built from few elemen-tary excitations emitted with well-defined wavefunctions. However, despite the realization ofsources generating quantized numbers of excitations, and despite the development of thetheoretical framework of time-dependent quantum electronics, extracting electron...

Strongly correlated low-dimensional systems can host exotic elementary excitations carrying a fractional charge $q$ and potentially obeying anyonic statistics. In the fractional quantum Hall effect, their fractional charge has been successfully determined owing to low frequency shot noise measurements. However, a universal method for sensing them u...

The original version of this Article contained an error in the author affiliations. Affiliation 3 incorrectly read “Centre de Nanosciences et de Nanotechnologies (C2N), CNRS, Univ. Paris Sud, Université Paris-Saclay, 91190, Saint-Aubin, France”. This has now been corrected in both the PDF and HTML versions of the Article.

Strongly correlated low-dimensional systems can host exotic elementary excitations carrying a fractional charge q and potentially obeying anyonic statistics. In the fractional quantum Hall effect, their fractional charge has been successfully determined owing to low frequency shot noise measurements. However, a universal method for sensing them una...

Defects in the hexagonal boron nitride (h-BN) layer can facilitate the tunneling current through thick h-BN tunneling barriers. We have investigated such current-mediating defects as local probes for materials in two dimensional heterostructure stacks. Besides IV characteristics and negative differential conductance, we have characterized the elect...

Defects in hexagonal boron nitride (h-BN) layer can facilitate tunneling current through thick h-BN tunneling barriers. We have investigated such current-mediating defects as local probes for materials in two dimensional heterostructure stacks. Besides $IV$ characteristics and negative differential conductance, we have characterized the electrical...

Competition between liquid and solid states in two-dimensional electron systems is an intriguing problem in condensed matter physics. We have investigated competing Wigner crystal and fractional quantum Hall (FQH) liquid phases in atomically thin suspended graphene devices in Corbino geometry. Low-temperature magnetoconductance and transconductance...

We have investigated the cross-over from Zener tunneling of single charge carriers to avalanche type of bunched electron transport in a suspended graphene Corbino disk in the zeroth Landau level. At low bias, we find a tunneling current that follows the gyrotropic Zener tunneling behavior. At larger bias, we find an avalanche type of transport that...

We demonstrate experimentally that composite fermions in monolayer graphene display weak antilocalization. Our experiments deal with fractional quantum Hall (FQH) states in high-mobility, suspended graphene Corbino disks in the vicinity of ν=1/2. We find a strong temperature dependence of conductivity σ away from half filling, which is consistent w...

We have investigated tunneling current through a suspended graphene Corbino disk in high magnetic fields at the Dirac point, i.e. at filling factor $\nu$ = 0. At the onset of the dielectric breakdown the current through the disk grows exponentially before ohmic behaviour, but in a manner distinct from thermal activation. We find that Zener tunnelin...

Quantum nanoelectronics has entered an era where quantum electrical currents are built from single to few on-demand elementary excitations. To date however, very limited tools have been implemented to characterize them. In this work, we present a quantum current analyzer able to extract single particle excitations present within a periodic quantum...

Shot noise measurements on atomic and molecular junctions provide rich information about the quantum transport properties of the junctions and on the inelastic scattering events taking place in the process. Dissipation at the nanoscale, a problem of central interest in nano-electronics, can be studied in its most explicit and simplified form. Here,...

Composite fermions in fractional quantum Hall (FQH) systems are believed to form a Fermi sea of weakly interacting particles at half filling $\nu=1/2$. Recently, it was proposed (D. T. Son, Phys. Rev. X 5, 031027 (2015)) that these composite fermions are Dirac particles. In our work, we demonstrate experimentally that composite fermions found in mo...

Competition between liquid and solid states in two-dimensional electron system is an intriguing problem in condensed matter physics. At high magnetic fields, the kinetic energy of electrons is suppressed, which favors Wigner crystallization of electrons to a lattice. However, electrons commonly favor an incompressible liquid state, the fractional q...

We have studied 1/f noise power SI in suspended bilayer graphene devices. Around the Dirac point, we observe ultra low noise amplitude on the order of f*SI/I2b=10−9 . The low frequency noise level is barely sensitive to intrinsic carrier density, but temperature and external doping are found to influence the noise power. In our current-annealed sam...

Using electrical transport experiments and shot noise thermometry, we investigate electron-phonon heat transfer rate in a suspended bilayer graphene. Contrary to monolayer graphene with heat flow via three-body supercollision scattering, we find that regular electron-optical-phonon scattering in bilayer graphene provides the dominant scattering pro...

One dimensional systems strongly enhance the quantum character of electron transport. Such systems can be realized in 5d transition metals Au, Pt and Ir, in the form of suspended monatomic chains between bulk leads. Atomic chains between ferromagnetic leads would open up many perspectives in the context of spin-dependent transport and spintronics,...

Using electrical transport experiments and shot noise thermometry, we investigate electron-phonon heat transfer rate in a suspended bilayer graphene. Contrary to monolayer graphene with heat flow via three-body supercollision scattering, we find that regular electron - optical phonon scattering in bilayer graphene provides the dominant scattering p...

Pt is known to show spontaneous formation of monatomic chains upon breaking a metallic contact. From model calculations, these chains are expected to be spin polarized. However, direct experimental evidence for or against magnetism is lacking. Here, we investigate shot noise as a potential source of information on the magnetic state of Pt atomic ch...

We present shot noise measurements on Au nanowires showing very pronounced vibration-mode features. In accordance to recent theoretical predictions the sign of the inelastic signal, i.e., the signal due to vibration excitations, depends on the transmission probability becoming negative below a certain transmission value. We argue that the negative...

For the study of junctions formed by single molecules shot noise offers interesting new information that cannot be easily obtained by other means. At low bias it allows, for some cases of interest, determining the transmission probability and the number of current carrying conductance channels. By this method it is possible to identify the cross-ov...

Generally, current shot noise is measured at low bias currents, and it reflects the transmission probability of the electrons. Here we present the first measurement at bias currents above the phonon energy of the system, i.c. a chain of Au atoms. The onset of phonon emission processes is signaled by an abrupt jump in differential conductance which...

Pt is known to show spontaneous formation of chains of metal atoms upon breaking a metallic contact. From model calculations these have been predicted to be spin polarized, which is reasonable in view of the Stoner enhanced susceptibility of bulk Pt and the increased density of states due to the reduced dimensionality. Here, we demonstrate that sho...

Activation of abnormal emitting sites in Carbon Nano Tube (CNT) field emitters and their elimination is reported. CVD grown, patterned CNT was used as cathode for field emission studies. We encountered the problem of current non-uniformity in CNT cathode. This non-uniformity was attributed to abnormally active emitting sites during voltage ramp-up....