Fish Symbolism in Indus Valley Epigraphy and Protohistoric Accounts

The contribution of the Indus Valley civilization to the historic cultures of South Asia is a matter of debate due to a discontinuity in material culture, from the time of its decline to the reappearance of urbanization several centuries later. Progress in the epigraphy of the Indus Valley has been hindered by the absence of a bilingual inscription and the brevity of its texts. One of the most frequent signs encountered in its undeciphered writing system is the pictogram of ‘fish’. On a few seal inscriptions, this sign appears alone, suggesting that it represented a meaningful word or a name. It is noteworthy that Indian literature of later centuries recounts a protohistoric kingdom named Matsya in the vicinity of the Indus Valley sites, as matsya is the Sanskrit word for ‘fish’ and a divinity in the form of a fish is celebrated in the Indian version of the flood myth. An analysis of these narratives is presented in this paper, revealing the possibility of an association with the Indus Valley civilization of the more distant past. These observations indicate that fish symbolism may have occupied a place of prominence in Indus culture from political and religious perspectives. The Matsya territory mentioned in Vedic and epic literature is discussed in light of the chalcolithic cultures of Rajasthan, and it is suggested that this region witnessed successive waves of migration of different cultural groups due to its economic importance related to the exploitation of copper reserves

Probing thermal expansion of graphene and modal dispersion at low-temperature using graphene NEMS resonators

We use suspended graphene electromechanical resonators to study the variation of resonant frequency as a function of temperature. Measuring the change in frequency resulting from a change in tension, from 300 K to 30 K, allows us to extract information about the thermal expansion of monolayer graphene as a function of temperature, which is critical for strain engineering applications. We find that thermal expansion of graphene is negative for all temperatures between 300K and 30K. We also study the dispersion, the variation of resonant frequency with DC gate voltage, of the electromechanical modes and find considerable tunability of resonant frequency, desirable for applications like mass sensing and RF signal processing at room temperature. With lowering of temperature, we find that the positively dispersing electromechanical modes evolve to negatively dispersing ones. We quantitatively explain this crossover and discuss optimal electromechanical properties that are desirable for temperature compensated sensors.Comment: For supplementary information and high resolution figures please go to http://www.tifr.res.in/~deshmukh/publication.htm

Spontaneous voltage peaks in superconducting Nb channels without engineered asymmetry

Rectification effects in solid-state devices are a consequence of nonreciprocal transport properties. This phenomenon is usually observed in systems with broken inversion symmetry. In most instances, nonreciprocal transport arises in the presence of an applied magnetic field and the rectified signal has an antisymmetric dependence on the field. We have observed rectification of environmental electromagnetic fluctuations in plain Nb channels without any asymmetry in design, leading to spontaneous voltage peaks at the superconducting transition. The signal is symmetric in the magnetic field and appears even without an applied field at the critical temperature. This is indicative of an unconventional mechanism of nonreciprocal transport resulting from a spontaneous breaking of inversion symmetry

Facile fabrication of lateral nanowire wrap-gate devices with improved performance

We present a simple fabrication technique for lateral nanowire wrap-gate devices with high capacitive coupling and field-effect mobility. Our process uses e-beam lithography with a single resist-spinning step, and does not require chemical etching. We measure, in the temperature range 1.5-250 K, a subthreshold slope of 5-54 mV/decade and mobility of 2800-2500 $cm^2/Vs$ -- significantly larger than previously reported lateral wrap-gate devices. At depletion, the barrier height due to the gated region is proportional to applied wrap-gate voltage.Comment: 3 pages, 3 figure

Magnetic field resistant quantum interferences in bismuth nanowires based Josephson junctions

We investigate proximity induced superconductivity in micrometer-long bismuth nanowires con- nected to superconducting electrodes with a high critical field. At low temperature we measure a supercurrent that persists in magnetic fields as high as the critical field of the electrodes (above 11 T). The critical current is also strongly modulated by the magnetic field. In certain samples we find regular, rapid SQUID-like periodic oscillations occurring up to high fields. Other samples ex- hibit less periodic but full modulations of the critical current on Tesla field scales, with field-caused extinctions of the supercurrent. These findings indicate the existence of low dimensionally, phase coherent, interfering conducting regions through the samples, with a subtle interplay between orbital and spin contributions. We relate these surprising results to the electronic properties of the surface states of bismuth, strong Rashba spin-orbit coupling, large effective g factors, and their effect on the induced superconducting correlations.Comment: 5 page

High Q electromechanics with InAs nanowire quantum dots

In this report, we study electromechanical properties of a suspended InAs nanowire (NW) resonator. At low temperatures, the NW acts as the island of a single electron transistor (SET) and we observe a strong coupling between electrons and mechanical modes at resonance; the rate of electron tunneling is approximately 10 times the resonant frequency. Above and below the mechanical resonance, the magnitude of Coulomb peaks is different and we observe Fano resonance in conductance due to the interference between two contributions to potential of the SET. The quality factor ($Q$) of these devices is observed $\sim10^5$ at 100 mK.Comment: 4 pages. Supplementary material at http://www.tifr.res.in/~nan