The S&P/ASX 300 Index (ASX: XKO) is sliding again today, adding to yesterday's 0.27% loss.

During afternoon trade, the ASX 300 is down a further 0.33% to 7,278.9 points. This means that the index has dropped around 3.5% since the start of September.

Let's take a look at which ASX companies are the strong performers today.

Australian Strategic Materials Ltd (ASX: ASM)

The Australian Strategic Materials share price is on the rebound, following a drop of 6% since Friday.

The rare earth metals company hasn't released any news in the past few weeks. However, a strong gain in the commodities markets could be a catalyst for its recent rise.

The spot price for rare earths mineral, neodymium, is fetching around 777,500 Chinese yuan per tonne, up 24.9% year-to-date.

Perseus Mining Ltd (ASX: PRU)

The Perseus share price is pushing higher with a 4.50% gain to $1.56.

The gold miner released an update today advising that it plans to hold a quarterly investor webinar on 21 October. Furthermore, Perseus will also provide more information on its Edikan and Yaouré exploration activities next week.

Investors appear to be buying up Perseus shares in expectation that positive results will come.

Zimplats Holdings Ltd (ASX: ZIM)

Also flying higher is the Zimplats share price, up 4.25% to $21.33 apiece.

The mining company hasn't provided the market with any new information in the past few weeks.

A possible catalyst for the upward trend could be the improvement in platinum prices since last Tuesday.

Now, let's take a look at the weaker ASX 300 companies.

Sezzle Inc (ASX: SZL)

Falling today is the Sezzle share price, down 6.46% to $5.65, with no new market announcements from the company.

Investors have sold off the buy-now pay-later (BNPL) company's shares after registering a 20% gain over the last 3 days.

Just last week, United States retail giant Target announced the launch of a BNPL offering in partnership with Sezzle. This service will be used to attract customers with affordable payment solutions.

Target is the eighth largest retailer in the United States and has a network of more than 1,909 stores. The deal could have a huge impact on Sezzle's bottom line for the future.

Yancoal Australia Ltd (ASX: YAL)

Another company's shares being weighed down by investors today is the Yancoal share price, down 5.10% to $3.91.

The energy producer's shares frequently make the ASX 300 headlines, bouncing from the top gains to biggest losers.

The spot price of coal has taken a break from its wild rise over the past 12 months, currently at US$244.50 a tonne.

It's worth noting that a number of ASX energy sector companies are also slipping into the red today. The S&P/ASX200 Energy Index (ASX: XEJ) is down 1.60% to 8,922.4 points.