arXiv subjects

M. Tomlinson

Publications and source records attributed to M. Tomlinson.

9 recordsLinked to original sources

arXiv2026

Emergence of a correlated insulating state in bulk 1T-NbSe$_2$ via metal intercalation

The 1T polymorph of NbSe$_2$, long confined to the monolayer limit, has remained inaccessible in bulk. Here, we report the realization of bulk 1T-NbSe$_2$ via electrochemical Sn intercalation. Transmission electron microscopy directly reveals the formation of the 1T structure induced by Sn intercalation. The intercalated samples exhibit insulating transport behavior, in stark contrast to metallic 2H-NbSe$_2$. Density functional theory calculations, however, predict a metallic band structure, highlighting the crucial role of emergent electronic correlations in the observed insulating state. Raman spectroscopy further reveals vibrational modes associated with Sn intercalation and possible charge density wave order. Our results establish electrochemical intercalation as an effective route to stabilize otherwise inaccessible bulk polytypes, positioning bulk 1T-NbSe$_2$ as a new platform for investigating correlated electronic states.

cond-mat.str-el↗

arXiv2025

Enhancement of the superconducting transition temperature due to multiband effect in the topological nodal-line semimetal Pb$_{1-x}$Sn$_{x}$TaSe$_{2}$

We report a systematic study of the normal-state and superconducting properties of single crystal Pb$_{1-x}$Sn$_{x}$TaSe$_{2}$ $(0\leq x \leq 0.23)$. Sn doping enhances the superconducting temperature $T_{c}$ up to 5.1 K while also significantly increasing impurity scattering in the crystals. For $x=0$ and 0.018, the specific heat jump at $T_{c}$ exceeds the Bardeen-Cooper-Schrieffer (BCS) weak-coupling value of 1.43, indicating the realization of strong-coupling superconductivity in undoped and slightly Sn-doped PbTaSe$_{2}$. Substituting Pb with more Sn lowers the specific heat jump at $T_{c}$ below the BCS value of 1.43, which cannot be explained by a single-gap model. Rather, the observed specific heat data of moderately Sn-doped PbTaSe$_{2}$ ($x= 0.08$ and 0.15) are reproduced by a two-gap model. Our density functional theory calculations suggest that three-dimensional Fermi pockets appear due to a reduction of the spin-orbit gap with Sn doping, and the multiband effect arising from these emergent Fermi pockets enhances the effective electron-phonon coupling strength, leading to the increase in $T_{c}$ of Pb$_{1-x}$Sn$_{x}$TaSe$_{2}$.

cond-mat.supr-con↗

arXiv2025

Hybridization between surface flat bands and bulk bands in the topological nodal-line semimetal Sn$_{0.15}$NbSe$_{1.75}$ probed via soft-point-contact spectroscopy

We report a detailed study of soft-point-contact spectroscopy of the superconducting topological nodal-line semimetal Sn$_{0.15}$NbSe$_{1.75}$ with the superconducting transition temperature $T_{c}=9.5$ K. In the normal state, we observe prominent asymmetric double peaks in the differential conductance $dI/dV$. The asymmetric $dI/dV$ curves are attributed to Fano resonance, quantum interference between two distinct tunneling paths of transmitting electrons into flat energy bands and dispersive bands. A phenomenological double Fano resonance model reveals the hybridization between these bands below the hybridization temperature $T_{\mathrm{hyb}}=23$ K. This hybridization drives an opening of a pseudogap below a characteristic temperature $T_{\mathrm{PG}}=6.8$ K. In the superconducting state, we observe an unusual upper critical field that increases linearly with decreasing temperatures from $0.4T_{c}$ to $0.01T_{c}$, suggestive of a possible exotic superconducting state. Our results suggest the presence of surface flat energy bands that stem from nontrivial topological nature of nodal lines in the bulk band structure and the hybridization between the surface flat bands and bulk bands in Sn$_{0.15}$NbSe$_{1.75}$.

cond-mat.str-el↗

arXiv2008

On the Weight Distribution of the Extended Quadratic Residue Code of Prime 137

The Hamming weight enumerator function of the formally self-dual even, binary extended quadratic residue code of prime p = 8m + 1 is given by Gleason's theorem for singly-even code. Using this theorem, the Hamming weight distribution of the extended quadratic residue is completely determined once the number of codewords of Hamming weight j A_j, for 0 <= j <= 2m, are known. The smallest prime for which the Hamming weight distribution of the corresponding extended quadratic residue code is unknown is 137. It is shown in this paper that, for p=137 A_2m = A_34 may be obtained with out the need of exhaustive codeword enumeration. After the remainder of A_j required by Gleason's theorem are computed and independently verified using their congruences, the Hamming weight distributions of the binary augmented and extended quadratic residue codes of prime 137 are derived.

cs.IT↗

arXiv2005

GF(2^m) Low-Density Parity-Check Codes Derived from Cyclotomic Cosets

Based on the ideas of cyclotomic cosets, idempotents and Mattson-Solomon polynomials, we present a new method to construct GF(2^m), where m>0 cyclic low-density parity-check codes. The construction method produces the dual code idempotent which is used to define the parity-check matrix of the low-density parity-check code. An interesting feature of this construction method is the ability to increment the code dimension by adding more idempotents and so steadily decrease the sparseness of the parity-check matrix. We show that the constructed codes can achieve performance very close to the sphere-packing-bound constrained for binary transmission.

cs.IT↗

arXiv2005

A New Non-Iterative Decoding Algorithm for the Erasure Channel : Comparisons with Enhanced Iterative Methods

This paper investigates decoding of binary linear block codes over the binary erasure channel (BEC). Of the current iterative decoding algorithms on this channel, we review the Recovery Algorithm and the Guess Algorithm. We then present a Multi-Guess Algorithm extended from the Guess Algorithm and a new algorithm -- the In-place Algorithm. The Multi-Guess Algorithm can push the limit to break the stopping sets. However, the performance of the Guess and the Multi-Guess Algorithm depend on the parity-check matrix of the code. Simulations show that we can decrease the frame error rate by several orders of magnitude using the Guess and the Multi-Guess Algorithms when the parity-check matrix of the code is sparse. The In-place Algorithm can obtain better performance even if the parity check matrix is dense. We consider the application of these algorithms in the implementation of multicast and broadcast techniques on the Internet. Using these algorithms, a user does not have to wait until the entire transmission has been received.

cs.IT↗

arXiv2005

Near Maximum-Likelihood Performance of Some New Cyclic Codes Constructed in the Finite-Field Transform Domain

It is shown that some well-known and some new cyclic codes with orthogonal parity-check equations can be constructed in the finite-field transform domain. It is also shown that, for some binary linear cyclic codes, the performance of the iterative decoder can be improved by substituting some of the dual code codewords in the parity-check matrix with other dual code codewords formed from linear combinations. This technique can bring the performance of a code closer to its maximum-likelihood performance, which can be derived from the erroneous decoded codeword whose euclidean distance with the respect to the received block is smaller than that of the correct codeword. For (63,37), (93,47) and (105,53) cyclic codes, the maximum-likelihood performance is realised with this technique.

cs.IT↗

arXiv2005

Improved Iterative Decoding for Perpendicular Magnetic Recording

An algorithm of improving the performance of iterative decoding on perpendicular magnetic recording is presented. This algorithm follows on the authors' previous works on the parallel and serial concatenated turbo codes and low-density parity-check codes. The application of this algorithm with signal-to-noise ratio mismatch technique shows promising results in the presence of media noise. We also show that, compare to the standard iterative decoding algorithm, an improvement of within one order of magnitude can be achieved.

cs.IT↗

arXiv2005

Idempotents, Mattson-Solomon Polynomials and Binary LDPC codes

We show how to construct an algorithm to search for binary idempotents which may be used to construct binary LDPC codes. The algorithm, which allows control of the key properties of sparseness, code rate and minimum distance, is constructed in the Mattson-Solomon domain. Some of the new codes, found by using this technique, are displayed.

cs.IT↗