arXiv subjects

Biman Jana

Publications and source records attributed to Biman Jana.

8 recordsLinked to original sources

arXiv2026

Structural Relaxation Enables Millisecond Infrared Photodetection in Selenium Iodine Semiconductors

The optoelectronic performance of amorphous and partially crystalline semiconductors is strongly governed by structural disorder, yet establishing direct correlations between structural evolution and carrier transport remains challenging. Here, we show that the solid state optoelectronic response of selenium iodine (SeI2) is dictated by its transformation from a metastable glassy phase into an ordered lamellar structure. Vertically resolved transport measurements reveal pronounced depth-dependent electrical conductivity within thick SeI2 films, arising from compositional and structural inhomogeneity developed during solidification. Immediately after solidification, the glassy SeI2 network exhibits sluggish carrier transport and persistent photoconductivity. Upon prolonged structural relaxation, however, the material undergoes significant transport enhancement, enabling millisecond-scale infrared photodetection with a response time of 4.3 ms, stable operation up to 8 kHz modulation frequency, and shot-noise-limited detectivities of 108 Jones at 1550 nm and 1011 Jones in the visible. Spatial photocurrent mapping demonstrates highly uniform carrier collection despite the self-assembled lamellar morphology, while infrared thermal imaging confirms practical imaging capability over a broad temperature range. These results establish structural relaxation as a powerful strategy for engineering carrier transport in selenium-based semiconductors and position SeI2 as a promising solution-processable platform for infrared photodetection and thermal imaging.

cond-mat.mtrl-sci↗

arXiv2011

Dynamic control of catalysis within biological cells

We develop a theory of enzyme catalysis within biological cells where the substrate concentration [S](t) is time dependent, in contrast to the Michaelis-Menten theory that assumes a steady state. We find that the time varying concentration can combine, in a non-linear way, with the ruggedness of the free energy landscape of enzymes (discovered both in single molecule studies and in simulations) to provide a highly efficient switch (or, bifurcation) between two catalytically active states, at a critical substrate concentration. This allows a dynamic control of product synthesis in cell.

cond-mat.stat-mech↗

arXiv2010

Dynamic coupling between the LID and NMP domain motions in the catalytic conversion of ATP and AMP to ADP by adenylate kinase

The catalytic conversion of ATP and AMP to ADP by adenylate kinase (ADK) involves large amplitude, ligand induced domain motions, involving the opening and the closing of LID and NMP domains, during the repeated catalytic cycle. We discover and analyze an interesting dynamical coupling between the motions of the two domains during the opening, using large scale atomistic molecular dynamics trajectory analysis, covariance analysis and multi-dimensional free energy calculations with explicit water. Initially, the LID domain must open by a certain amount before the NMP domain can begin to open. Dynamical correlation map shows interesting cross-peak between LID and NMP domain which suggests the presence of correlated motion between them. This is also reflected in our calculated two dimensional free energy surface contour diagram which has an interesting elliptic shape, revealing a strong correlation between the opening of the LID domain and that of the NMP domain. Our free energy surface of the LID domain motion is rugged due to interaction with water and the signature of ruggedness is evident in the observed RMSD variation and its fluctuation time correlation functions. We develop a correlated dynamical disorder type theoretical model to explain the observed dynamic coupling between the motions of the two domains in ADK. Our model correctly reproduces several features of the cross-correlation observed in simulations.

cond-mat.stat-mech↗

arXiv2010

Role of water in the enzymatic catalysis: study of ATP + AMP -> 2ADP conversion by adenylate kinase

The catalytic conversion ATP + AMP -> 2ADP by the enzyme adenylate kinase (ADK) involves the binding of one ATP molecule to the LID domain and one AMP molecule to the NMP domain. The latter is followed by a phosphate transfer, and then the release of two ADP molecules. We have computed a novel two dimensional configurational free energy surface (2DCFES), with one reaction coordinate each for the LID and the NMP domain motions, with explicit interactions with water. Our computed 2DCFES clearly reveals the existence of a stable half-open-half-closed (HOHC) intermediate state of the enzyme. Cycling of the enzyme through the HOHC state reduces the conformational free energy barrier for the reaction by about 20 kJ/mol. We find that the stability of the half-open-half-closed state (missed in all earlier studies with implicit solvent model) is largely because of the increase of specific interactions of the polar amino acid side chains with water, particularly with the arginine and the histidine residues. Free energy surface of the LID domain is rather rugged, which can conveniently slow down LID's conformational motion, thus facilitating a new substrate capture after the product release in the catalytic cycle.

cond-mat.stat-mech↗

arXiv2010

Propagating rotational jump events drive liquid-liquid transition in supercooled liquid water

We observe, at low temperature, the appearance of propagating events that originate from the inter-conversion between adjacent four and five coordinated water molecules in supercooled liquid water, resulting in the migration of the coordination number five in a string-like fashion, creating rotational jumps along the way. The length of the connected events increases with lowering temperature. Each propagation event is terminated by a 3-coordinated species, present in a small number at large supercooling, which interacts cooperatively with 5-coordinated molecules to annihilate both the species. We find that these growing dynamical correlations manifest in a divergent-like growth of a non-linear density response function, \times4(t), which is given by a four point time correlation function (FPTCF). The locus of the maximum of \times4(t), when plotted against the time t* of maximum, exhibits a sharp peak precisely at the temperature where the static response functions (specific heat, isothermal compressibility) also show similar sharp, divergent-like, peak. While the decay of population fluctuation time correlation function of both 4- and 5- coordinated species slows down dramatically and a step-like feature of the relaxation becomes evident, the lifetime itself of 5-corrdinated species remains short. These results suggest a new molecular mechanism of low temperature anomalies and of the liquid-liquid transition in terms of initiation, growth and termination of propagating jump and inter-conversion events.

cond-mat.stat-mech↗

arXiv2008

Dynamical transition in translational and rotational dynamics of water in the grooves of DNA duplex at low temperature

We have simulated structure and dynamics of water in the grooves of a DNA duplex using moleculear dynamics simulations. We find signatures of a dynamical transition in both translational and orientational dynamics of water molecules in both the major and the minor grooves of a DNA duplex. The transition occurs at a slightly higher temperature ($T_{GL} \approx $ 255 K) than the temperature ($T_L\approx$ 247 K) where the bulk water is conjectured to undergo a dynamical transition. Groove water, however, exhibits markedly different temperature dependence of its properties from the bulk. Entropy calculations reveal that the minor groove water is ordered even at room temperature and the transition at $T \approx$ 255 K can be characterized as a {\em strong-to-strong} dynamical transition. The low temperature water is characterized by pronounced tetrahedral order, as manifested in the sharp rise near $109^{\circ}$ in the O-O-O angle distribution. We find that Adams-Gibbs relation between configurational entropy and translational diffusion holds quite well when the two quantities are plotted together in a master plot for different region of aqueous DNA duplex (bulk, major and minor grooves) at different temperatures. The activation energy for the transfer of water molecules between different regions of DNA is found to be independent of temperature.

cond-mat.soft↗

arXiv2007

Orientational relaxation in a discotic liquid crystal

We investigate orientational relaxation of a model discotic liquid crystal, consists of disc-like molecules, by molecular dynamics simulations along two isobars starting from the high temperature isotropic phase. The two isobars have been so chosen that (A) the phase sequence isotropic (I)-nematic (N)-columnar (C) appears upon cooling along one of them and (B) the sequence isotropic (I)-columnar (C) along the other. While the orientational relaxation in the isotropic phase near the I-N phase transition in system (A) shows a power law decay at short to intermediate times, such power law relaxation is not observed in the isotropic phase near the I-C phase boundary in system (B). In order to understand this difference (the existence or the absence of the power law decay), we calculated the the growth of the orientational pair distribution functions (OPDF) near the I-N phase boundary and also near the I-C phase boundary. We find that OPDF shows a marked growth in long range correlation as the I-N phase boundary is approached in the I-N-C system (A), but such a growth is absent in the I-C system, which appears to be consistent with the result that I-N phase transition in the former is weakly first order while the the I-C phase transition in the later is not weak. As the system settles into the nematic phase, the decay of the single-particle second-rank orientational OTCF follows a pattern that is similar to what is observed with calamitic liquid crystals and supercooled molecular liquids.

cond-mat.soft↗

arXiv2007

How glassy are orientational dynamics of rodlike molecules near the isotropic-nematic transition?

In an attempt to quantitatively characterize the recently observed slow dynamics in the isotropic and nematic phase of liquid crystals, we investigate the single-particle orientational dynamics of rodlike molecules across the isotropic-nematic transition in computer simulations of a family of model systems of thermotropic liquid crystals. Several remarkable features of glassy dynamics are on display including non-exponential relaxation, dynamical heterogeneity, and non-Arrhenius temperature dependence of the orientational relaxation time. In order to obtain a quantitative measure of glassy dynamics in line with the estbalished methods in supercooled liquids, we construct a relaxation time versus scaled inverse temperature plot, and demonstrate that one can indeed define a 'fragility index' for thermotropic liquid crystals, that depends on density and aspect ratio. The values of the fragility parameter are surprisingly in the range one observed for glass forming liquids. A plausible correlation between the energy landscape features and the observed fragility is discussed.

cond-mat.soft↗